Supposedly the original Sad Ghost guy died a while back, so people put them up as sort of a tribute all over the east coast. I've seen them as far south as Richmond, VA, and I used to see them everywhere around town when I lived in Philly. I would assume the artist had some connection to Philly - there's one of them on a railway embankment near Sullivan that's superimposed on a map of Pennsylvania with a little heart on Philly.

There's a TON of them around metro west right now, so I assume someone local is doing it as a tribute or something.