Hello! I have some experience with lasers, so I thought I would point out this video:
The following video is of a laser projector projecting on to clouds. Notice that the beams are hardly visible until they hit the clouds, and then
they become very clear:
www.youtube.com...
(sorry couldn't embed it)
The lasers don't appear to flicker to the naked eye like they do in the video.
I am not saying that this is what happened in Las Vegas, but it is possible to project fairly clear images onto clouds using lasers, although the
lasers needed are extremely powerful (the one in this video is 40 watts - that's 8000 times more powerful than a normal laser pointer, which is .005
watts!)
The one problem with this laser explanation is the fact that you said no light source was visible. The laser beams should be visible, but in an an
area with as much light pollution as Las Vegas, it is possible they could be obscured.
Also, with laser beams, the farther away from the light source you are, the less visible the beams become (but the projected image stays the same
brightness)
Heres a picture I made sort of describing this:
So finally, my conclusion is that while it is possible to use lasers to achieve a similar effect to what you're describing, it is unlikely that
lasers were used. So as far as I'm concerned, this remains unsolved
Even though this doesn't help to solve this mystery, I hope everyone has learned at least a little about lasers!