Aliens in GTA 5

Midst a hodgepodge of GTA 5 Alien sightings, UFO appearances, Flying Saucers, and jetpack rumors, a tantalizing unsolved mystery continues to frustrate players. 

What Do These Symbols Mean? 

Explorers have found spacecraft hovering over mountaintops and concealed in the skies high above significant landmarks. After meeting Omega in the desert, a series of glowing, pulsing Spaceship Parts appear scattered throughout San Andreas. Tracking them down leads to the creation of a tiny spacecraft, and unlocking of the Space Docker.
But none of this explains GTA 5's greatest unsolved mystery: the meaning of the three most prominent Glyphs on a map painted atop Mt. Chiliad.

The Truth is Out There, Somewhere

For months, dedicated GTA 5 players have combed the map of San Andreas amassing clues, searching for anything which might explain the meaning of the glyphs. Online communities have grown up around the mystery, with members swapping notes, exchanging discoveries, and systematically testing, substantiating, and debunking theories.
Recently, dedicated players have used exploits to spawn Vehicles under the map. Using their new-found mobility, they have discovered hidden FIB textures beneath the Mt. Chiliad platform and strange objects beneath Ft. Zancudo. [1]
Increasingly, the indications are that the mystery will be explained or developed in some form of upcoming DLC or special event, as exhaustive exploration has provided no key to unlocking the mystery. There's obviously something going on, but there appears to be no in-game mechanism for legitimately unlocking the hidden material.

The Beginning of the Search

A cryptic painting on the wall of the Cable Car station atop Mt. Chiliad was one of the earliest sources of intrigue for GTA conspiracy-hunters.The main map is remarkably similar to the shaft and chamber layout of a pyramid, suggesting the possible existence of a subterranean dungeon. Also scattered around the image are a number of smaller markers. While the meaning of many of the symbols within have been encrypted, the large icons of cracking egg, a spaceship, and a humanoid form remain an intriguing puzzlement.
The symbol matches the UFO depicted in the Cable Car station painting. On the back of the platform it reads "Come back when your story is complete."
The carefully hidden painting beneath the platform atop Chiliad’s highest point is the sighting point for a well-documented postgame Flying Saucer appearance, which takes place late at night during thunderstorms. Other symbols likely indicate other known Glyphs spaced around the mountain. The evidence strongly suggests a relationship between the pen15 mountain and the mysterious uninterpreted Glyphs
Some players speculate that the Mt. Chiliad Map should be laid over the GTA 5 pack-in paper map to reveal a number of significant locations. Current efforts center around centering the map above the northward edge of the island, though this produces no discernible explanation for the three main Glyphs.
An alternate  theory (image below) involves lining up the eye at the top of the mountain (red dot) with the glyphs on the the side of the mountain (green dots) leaving one half faded glyph (green circle).

Image Provided by GTA Forums

Glyphs line up as per the image below. 
While intriguing, these theories fail to address the purpose of the connecting lines between Glyphs, as well as the three large symbols.

Alien Flying Saucers

To date 4 confirmed UFOs have been located in GTA 5. Details on each are available at UFOs. Most pertinent to the search is the presence of a UFO directly over Mt. Chiliad, appearing in the rain at 3 AM after 100% completion. 

The Search for Underground Tunnels at Mt Chilliad

Recent reports of players using clipping glitches to gain access to the inside of the mountain to show tunnels have mostly been dismissed as known and already accessable tunnels:

• The Road Tunnel joining Paleto Bay to the Alamo Sea

• The Rail Tunnel joining Paleto Bay to the Alamo Sea

• The Road Tunnel that passes under the runways at Fort Zancudo

Though the hunt still continues as tunnels are not made visible until in close proximity. Current searches are revolving around the Saw Mill drain grates.

The Jetpack Connection

Online communities of UFO hunters have focused largely on a resemblance of the humanoid glyph to a person riding a jetpack. Many people believe that unlocking the riddle of Mt. Chiliad will unlock access to this GTA unicorn item.

New Clues and Current Speculation

The UFO hippie camp near Sandy Shores is ringed with a trail of Alien script. Some players believe the script might contain a decipherable code, others believe it to have ties to Yoga positions which are themed throughout the camp
The breaks between examples below are limited by video capture capibilities, not by any distinctive breaks in the text. Viewed left to right from the outside of the ring, the code reads:
 

Possible Alien Code Part 1

Possible Alien Code Part 2

Possible Alien Code Part 3

Possible Alien Code Part 4

Possible Alien Code Part 5

Possible Alien Code Part 6

Possible Alien Code Part 7

Possible Alien Code Part 8

Possible Alien Code Part 9

It's also possible that the code reads from the inside of the ring, in which case the images would be flipped and the order reversed. 

Other Alien Stuff

These flying saucers aren't the first hint of extra-terrestrial life in GTA 5. The GTA 5 Special Edition map includes a UFO part location revealed by exposure to black light.
Alien Glyphs are concealed throughout the map, including drawings on Mt. Chiliad, near the Altruist Camp, and at the Hippie Camp. 
Aliens also make cameo appearances frozen in ice in the Prologue Mission and wandering the lots of the movie studio. 
Aliens are also seen several times during hallucinations by Michael and Trevor. . What does this mean? Is there a secret cavern beneath Chiliad? If so, how does one access it? Or is it a deliberate red herring? When we know, you’ll know, gentle readers.Check back often for updates, and add your own discoveries to the GTA 5 Wiki.