Red Envelope Madness!
I don't know about 'postal graffiti' either!What is it? Do people draw on their stuff and then send it out?It looks wicked cool.
Sounds right to me. I think the Flickr-user who uploaded the photo invented the term.
Awhile ago there were 2 guys who did a bunch of fake postal stamps and had a gallery show of the envelopes with the cancelled stamps.