In my area it's illegal to post signs on poles and other street signs, only your own property... but that property can be your car like AG did (well, not necessarily
that big). I've seen police just go around and take down peoples' garage sale signs. Oh, and you have to have a permit prior to the sale date.
Years ago I used to go to lots of garage sales looking for specific things and got lucky many times... i.e. one pair of old Levi's - .50 cents, I turned around and sold them for $475.00. Good times
