Are there any legal restrictions against me holding a sign along the road?

So I have some friends going back to their first day of school tomorrow morning and I’d like to hold up signs along the road, near but not on school property so the kids in the buses can see. Nothing inappropriate, just fun signs. I live in Pennsylvania and the school is in a rural area. I’m not concerned with getting in trouble as much as I am knowing my rights. If anybody has insight it’d be greatly appreciated. Thanks guys