Kilroy was Here

According to Wikipedia, "Kilroy was here is an American popular culture expression, often seen in graffiti. Its origins are debated, but the phrase and the distinctive accompanying doodle—a bald-headed man (possibly with a few hairs) with a prominent nose peeking over a wall with the fingers of each hand clutching the wall—is widely known among U.S. residents who lived during World War II."

Other than the fact that Mark isn't a bald-headed man with a prominent nose, the image is similar

The sign will eventually be installed right above the awning, but for now Mark is going to stand on the roof and hold it :-)