Robert Patrick also shows up as a cop in the Schwarzenegger movie "The Last Action Hero". They walk right past him, and I think Arnold does a quick take in passing.
I call bits like that "handshakes", since they're meant for people who know a bit of the filmography of the actors.
Another one like that is in "The A-Team", when Dirk Benedict is on a Hollywood back lot and walks past a guy in a cylon costume, and gives the guy a double take.