The orbs have been spotted on several occasions above Sin City, with the most recent sighting coming in April .
And some think they have now returned, with footage showing three dazzling lights slowly moving across the night sky.
The video, posted to YouTube channel WP Oreo, shows the trio of orbs moving in a triangular formation.
It seems like it is a solid shape but the lights then change shape and move into a straight line.
They also appear to flash in the sky. Thousands of people have seen the video and many reached for the extraterrestrial explanation.
“Okay I am ready to be probed,” he wrote.
Another added: “The aliens are coming.”
Many suggested they were drones, but this was dismissed by one “expert” who wrote: “As a licensed and experienced drone enthusiast, there’s one part of the video that caught my attention and that’s the ending.
“Drone lights are typically LED and so they are either on or off. They don’t flutter and reduce light output and fade.”
But others believed the orbs could simply be helicopters with searchlights.
One said they could even hear the rotor of a helicopter, although the uploader claimed that came from an aircraft flying over their house.
It comes after a cigar-shaped object was seen flying behind an NBC news broadcast.
Meanwhile, crystal-clear footage captured an unknown “craft” hurtling across the face of the moon.