This billboard attempts to play off the cultural phenomenon of billboard hacking, the art of modifying billboards, usually to make politcal or social statements.
This billboard is a wink and nod at billboard hacking. It's not a bad idea; someone hijacks a jewelry-store billboard to propose to his sweetie. It slips in the suggestion of romantic love in a very elegant way.
They blew it.
Had they just done the billboard as if it had been hacked, it would've worked quite well. But they chickened out. I can just see the conversation: "But what if someone thinks the billboard was really hacked?" The answer, of course, is that the billboard would be even more effective...but no. They didn't want to take the chance that someone somewhere might think the billboard wasn't exactly as the jewelry store wanted it to be, so they added a picture of the guy "painting" the billboard.
Now it's just another lame billboard.