I'm sending Aiyume the picture I did for our trade, so I did a little doodle on the mailer. I liked it so much, I thought I'd submit it!
I think getting mail is one of the best things... It's much more personal than an email. So, whenever I send out something in the mail, I try to make it a little special. I include a hand-written note, I usually include another doodle, and I draw on the mailer or envelope.
Anything I can think of that would make the other person's day a little brighter. :)

Literally a 5-minute doodle with micron and prisma marker.

Syrpolis©Aiyume
Art by me!