The project is titled 'A Love Letter For You' and is essentially ~50 love-themed murals on rooftops and buildings throughout Philly with an old-school signage twist. It's not the graffiti you're used to seeing and I'm enamored with it to no end.
He's also made a book about the project and is having a release party this weekend complete with tattoo-shop takeover and guided tour of said murals just in time for Valentine's Day. Whether or not I make it down there will depend heavily on the weather and the company willing to join me, but for any interested parties in the Philly area here's the info:

More info on his site.