The notes read: "I will not stay away from your kids. Your friend, Pervert."
Two of them have wound up in Kennebunk and one was dropped off in Arundel.
"You've got somebody lingering around the bush hiding and putting notes in your mailboxes waiting for your kids to come out. Gadzooks, that's crazy," Kennebunk resident Ginger Nadeau told CBS Boston.
An image of the man was captured by a security camera and police say that "he has a distinctive walk" and that he swings "his arm forcefully," the Bangor Daily News reported.
If the notes are some sort of attempt at humor, Kennebunk Police Chief Bob MacKenzie isn't laughing in the slightest. "If they're doing it as a joke, it's a sick joke. Obviously as a father myself you see a note like that and it's very concerning," he said.
It's not clear what charges the man would face if he is caught, but extra patrol units have been added in the area to hopefully bring him in as soon as possible.
"Keep an eye out for anything suspicious," said KPD Lt. Dan Jones, "and report anything to police immediately."