I drive a long way to work and back, about 45 minutes over about 35 miles (~55 km). Much of it is rural and all of it is along a major highway. There are advertizing billboards.
The ones for rent have a telephone number on them (not strange), but the number looks like it hasn’t been updated since 1960-something since the exchange is still given using two letters!
Several others are just big letters on a solid background to promote this website: http://worldpeace.org/ (I have no idea)
Two of them are downright dubious. One is higher up on a hillside and covered by trees in the summer. All it says is “BLOOD”.
The second one used to be an ad for the Boy Scouts, only it has been mostly painted out and just says “WANTED, BOYS”. Creepy.