He probably put the sign on the public easement in front of his home. Cities and villages routinely remove any signs put on any such public property. However, if the sign was up on the man’s front lawn the city would have no right to remove his sign.
Don't think this is entirely correct as easements gives the access rights to the target, not the source. It would all be spelled out in the easement as there aren't any specific easement laws -- they are all custom in one way or another.
My city called me up one day (Oceanside, CA) and said they wanted 4' easement on the back of my property so they could widen the road and install a right turn only lane 1 block down before my house. Since the city actually wanted to asphalt over the 4' and allow cars to use it, my lawyer said it's not an easement so the city couldn't force the issue. It died because the city can't force an easement without consideration, and they didn't want to give any consideration. I guess all contracts need considerations from both sides.
Home repair companies always put advertising signs out in front of houses when they do jobs, and the cops never remove them. They are every bit as much an eyesore as this person's sign. There's obviously something else going on here.