Stop signs are payed for with stolen money. in a way that stop sign belongs to you more than it does the people who actually claim ownership of it.
Oh lawdy, one of you people.
Alright, let's assume I'll go along with the whole "taxes are theft" thing, and that sign does indeed belong to you. It also belongs to everyone else in the town.
You wouldn't stick crap on other people's things, so why stick it on people's shared things, especially since it'll be removed at your cost via taxes/stolen money.