Well, the flag part is irrelevant to me. I don't care if you put that card on a $100 bill and left it on my property it's my property, don't put your crap on it without asking me first. And don't come knocking on my door to ask me either, I'm busy and don't feel like getting my lazy-a55 up to come talk to you. Bottom line, just go away. If you want to advertise use the post office or tv or radio like you are supposed to.
Edit: And just because the easement is not completely mine, unless you are the government or utility company, don't put your crap there either. It's more mine than yours.