In almost every city and county in the US, it’s illegal to place political signs in the public right-of-way. Even tree lawns in the public right-of-way are off-limits. Enforcement varies, of course.
At my first real job, one of my duties was sign code enforcement. During election season, every day I’d take a city truck and make the rounds, pulling up illegally placed political signs. I kept track of the candidates whose signs were yanked, because there was the inevitable accusations that I was biased towards one side or the other. Even after sending guides to campaign offices describing the rules for proper sign size and placement, every year hundreds of signs would get placed in medians, inside the loops of cloverleaf interchanges, public parks, and so on.
I noticed that in the recent election, there’s a disproportionately large number of Ron Paul signs that were placed in the public right-of-way, hanging from overpasses, and so on. They never seem to be removed.