When staying at Mandalay it seems like a pretty obvious thing to do to walk down to the famous Vegas sign. It's a short (15-20) walk from Mandalay. The only real problem is that the sign is in the middle of the strip and there's no lights/crosswalks so if you walk it you need to run across the street to get to the sign.
It was pretty busy on a Monday morning and there were a couple locals offering to take your picture with your camera, and for a couple bucks who can argue?
All in all, I'm glad I finally made it down here!