HUGE WALL OF TEXT ABOUT THIS WHOLE DAMN THING!
It's a big wall of text but please read it. Then feel free to repost, reformat or argue.
DON'T QUOTE THE WHOLE DAMN THING THOUGH!
This is the mural on the top of Mt Chiliad. The mountain is shown in profile from roughly the north western side of the map. The Xes show the locations of glyphs painted on the mountain.
OVERLAYS DO NOTHING UNLESS THE MURAL IS OVERLAYED OVER THE NORTH WESTERLY SIDE OF THE MAP. THIS ONLY SHOWS THE LOCATION OF THE GLYPHS. HUNDRED'S OF OTHER OVERLAYS HAVE BEEN TRIED AND THEY REVEAL NOTHING.
The glyphs show conditions that must be met for a UFO to show on the top of the mountain (indicated by the UFO symbol at the top of the mural).
Going Clockwise from top left
Rain It must be raining
Path You must travel to the top of the mountain to see the UFO
Moon You can only see it at night. In this case at 3am (please Google this time as real life studies show that this is when weird things happen!)
Worn glyph You need 100% completion or you won't see it
UFO You need to stand on the red UFO symbol.
If you meet all of these conditions, you will see a UFO from the viewing platform at the top of Mount Chiliad. You cannot interact with this in any way and it disappears if you get too close and is also impervious to gunfire/explosions/etc.
The symbols at the bottom may not represent rewards or unlockable items. People have theorised that they represent locations, rewards, DLC items, characters, etc. but no theory has been based upon fact, only on opinion. It is also possible that these symbols represent the locations of other UFOs.
There are a few other UFOs in the game.
Northeast of Paleto Bay is an underwater UFO. This may be the UFO Omega referred to, it might not. You will likely come across this when collecting nuclear waste. It cannot be interacted with.
Sculpture Park/Hippy Camp
In Sandy Shores is a representation of Salvation Mountain, an adobe art installation in the desert. This design is influenced by the new age and alien greys movement. A UFO shows above the red glyph on top of the smaller of the two sculpture hills but you can only see this if you take a helicopter to maximum height.
The UFO is the same design as the Mt Chiliad UFO and has the writing FIB on the side. It cannot be interacted with but does not disappear when you approach it.
There are copies of the glyphs on the side of Mount Chiliad at the Sculpture Park. It is likely these were designed by the hippies at the camp as shown by the number of paint cans lying around.
There are also a number of other decorations around the camp such as crop circle designs, aliens having sex, graffiti. These are purely for decoration. Many people have tried to translate these to no avail so it is confirmed that they have no meaning other than to look nice. These decorations also appear in other places around the map, again for decoration only.
The car with a UFO on it is at the camp and this cannot be interacted with.
At 3am, a green light shines on top of a bunker at Fort Zancudo. At the same height as the Sculpture Park UFO, a UFO of a different design flies. This is a prototype stealth plane designed by the military as has featured in real life. This can be confirmed as it flies above a military air base; it is military green and also has writing in English on it. This writing says 'segregate and rearrange'. If you rearrange the letters in segregate, you get Easter Egg, showing that this UFO and all others are Easter Eggs.
The UFO cannot be entered or interacted with and, like all UFOs, is impervious to damage/gunfire/explosions/etc.
Areas of note
The Altruist camp is covered in graffiti that represents the sun and stating 'He is risen' and 'embrace the light'. The Altruist website states that they hate the sun, so something has changed for them but no-one knows what. People believe the sacrificial stone has a symbol of the Jetpack stickman on it, but this is just a vague outline given by the texture of the rock.
A crate also appears here when Trevor is abducted by the Altruists, but this is to act as cover as Trevor shoots his way out. Investigations are on-going on site to see if the barn contains an item.
People have tried to sacrifice people and animals on the stone slab but this did not work.
There is a cave under the camp on the side of the hill which contains some more graffiti, a ram's skull and a burning barrel. The skull and fire is a reference to the game Dark Souls. The graffiti is representative of that found in the camp.
Chiliad - Misc. -
The doors in the tunnel by Mount Chiliad are just decorative. All of the road tunnels have these fire exits.
The door in the cable car house at the summit is also just decorative. That room would contain the motors, etc.
There is a control tower in the Fort which can be entered and contains a mini-gun. There is a lift which is inoperable. The tower is enterable as it is a location used in a GTAO mission.
There is a lift in the bunker that the green UFO light shines on. This has been stated to open under certain conditions (snowy weather cheat active) but leads nowhere. Again, this is likely used in a GTAO mission.
The observatory has statues similar in shape to the glyphs on Mt Chiliad. There is nothing further on site.
Maze Bank/FIB Building/Anywhere in the city
These buildings often have references to Eyes or the UFO shape in their architecture, but these are just references to the Illuminati. IRL it is believed that the Illuminati is in control of banking institutes and the government so it makes sense that references to them would be included in their architecture (see the order of Freemasons and their role in architecture through a simple Google search). These references have no further involvement in the mystery.
The lighthouse light can be controlled by pointing your gun at it. No use has been discovered for this.
Humane Research Labs
This featured in a mission and doesn't have any further use. No clues, hints or mysteries abide here.
No other mountains have any relation to this mystery.
These appear at cafes and buildings across the map. Some make noises, some don't. They're just statues (although it's interesting that they are similar to the three symbols at the bottom of the Chiliad mural).
The Special Edition Blueprint Map
Did you buy the special edition of GTA V? You got a nifty blueprint map. Hold it under a UV light and you'll see the character Trevor has written on it. He has indicated a list of collectible items (for collectible missions in GTA V); shops that can be robbed and houses that can be bought in GTAO and also collectible weapons and armour. He has done this by either drawing a symbol or writing a phrase such as 'Shoot for the stars' to signify a gun is at the observatory. These phrases and symbols have NO further meaning.
On the back of the map is a series of directions and instructions. It is not understood what these are for but is believed to be a hint to buy the sonar collections dock. However, the amount stated on the map and the cost of the docks does not add up.
The Epsilon cult
This fake religion was first introduced in GTA SA and now appears as a series of missions for Michael. This cult is a spoof of faux religions such as scientology. The teachings, hints and clues provided within these missions are representative of the same type of beliefs as scientology and should NOT be misconstrued to be hints as to Easter eggs in the game world. In fact, the whole idea of the cult is to convince a person to believe these poor metaphors have some meaning when, in fact, they don't.
Other Easter eggs
There are a number of other Easter eggs which have no relation to the UFO mystery. There is a thread dedicated to Easter eggs, go view it
Infinite 8 serial killer Ghost Bigfoot Sea Monster
Hey, including the UFOs, these are all things that were myths in GTA SA. Now they're real eggs!
It does f*ck all. Just enjoy it.
The Space Docker and Epsilon Tractor are just rewards and have no relevance to any mystery. EVERYTHING that you can think of has been tried, especially relating to the Space Docker.
Bodies of water
ALL of the lakes, ponds, reservoirs, etc. have been checked. There's nothing in there.
Please understand the concept of mise-en-scene, that is, the items on screen that serve to make the game world have more verisimilitude (be more real). The game world has lots of graffiti, paintings, artwork, statues, character scripts, random events, etc. which all serve to make the game world real.
Hardly anything in the game is a clue to a mystery.
Things which aren't include
Any type of decoration around the Sculpture Park (apart from the glyphs)
Any sculpture or painting which features an eye (just a nod to the Illuminati)
The agents hanging around the desert or radio shack.
Any type of graffiti.
ALL of these things and more have been found, theorised over and proven wrong or proven to work. There have been a total of 5 weeks working on this and well over 600 pages on this forum dealing with the mural, the UFOs and other mysteries.
What can be confirmed
There are UFOs
You can't fly them
Interiors do not load unless you trigger them correctly so glitching is not a way to prove or disprove anything
The weather cheat will still load the Chiliad UFO.
The jetpack has not been found and it is very likely it does not exist.
Mine doors and sewer grates cannot be opened and have nothing behind them (this may change if a trigger is found to open them).
There are only three flying UFOs and only two stay when you approach them.
The majority of the graffiti, set decoration, etc. is just to add to the themes underlying the game.
The themes are Aliens, Illuminati, NSA style government monitoring & government corruption.
Other Easter eggs exist and are not related to the UFO mystery/Chiliad Mural.
There, that's it! Thanks for reading. Please repost this, reformat it, whatever you like. Please do disagree if you like BUT please make sure you've read both Jetpack threads and both Chiliad Mural threads FULLY before doing so. That way you get the full picture.