Locations:
UFOs can be spotted at specific times and locations, often in remote areas like the Everglades or Kelly County. One notable sighting occurs near the 'Conspiracy Theorist's' hangout on Vice Beach at 3 AM on clear nights.
Interaction:
They are usually non-interactive, flying overhead or hovering briefly before disappearing. Photographing them can sometimes trigger unique dialogue from your characters or unlock a specific 'Strangers & Freaks' mission.
Significance:
Primarily an easter egg, but some sightings are tied to the 'Conspiracy Theorist' side questline, offering unique rewards upon completion.