I'm sure I'm not the first to notice this, but have you guys noticed the Marvel character symbols on this cover (http://images3.wikia.nocookie.net/__cb20120214211909/batman/images/c/ce/Nightwing_Vol_3-6_Cover-1.jpg
). Nightwing is, essentially, kicking the collective asses of Spider-Man, Captain America, The Punisher, and someone else...maybe GhostRider?
It got me wondering, are there other examples of this kind of thing? DC "characters" appearing on Marvel covers, or vise versa?