Interesting that I've tracked down the code enforcement group here in Clark County. They have said, repeatedly, and with much gusto, DON'T REMOVE THEM. Instead, take a picture and mail it or give them a call. They will note the location, and use the law to get the name/address of the person who posted them, and consequently, serve them with $100 fines for each sign they find.
They say they do this with great results, and have put a stop to much of it in many neighborhoods. A missing sign is nothing next to a missing sign and a knock on the door and cash out of your already failing business!
So, though I'd love to take them down, I'm instead making a nice little placard with the words "HerbaLife", "MLM" and "I AM LITTER" cut out of it. I'll place these over the signs, use my flourescent green $3 can of paint and hit the 10 or so I know about in my neighborhood.