There's nothing stopping people from removing those signs. Either trashing them as litter or returning them to the people that put them there.
GoDan, aren't you one of those anti-big government guys? Yet your solution is to get government to make and enforce a penalizing law to take care of a problem that you could easily resolve on your own. Without spending taxpayers money using legislators and law enforcers time in making and enforcing something that any concerned citizen can easily do without any assistance from government.
People throw litter on the side of the road in front and on the side of my house everyday. I suppose I could grab their garbage, jump in my car, chase them down an throw the litter back to them. Or I could police the property 24/7 write down and report them to DOT for littering. Would that solve the litter problem? No. It would only create other problems for me and my government.
Why in the hell complain about something you can fix yourself?
Time & Tide Changes Everything