Marta,
My next door neighbor has a hanging yard sign to advertise his studio. But he's not a portrait artist per se. The sign is basically one of his paintings. If it weren't hanging in his yard, it could just as easily hang in a gallery. See his work at
www.schex.com
It's held up pretty well to our non-stop rain here in Louisiana. On his previous home (just down the block) he had murals on the exterior walls. He's married with children now, so he paints more on canvas and less on the house.