TerrenceIsTheMann said: "Don't stage door if you're not seeing the show. Don't. It's meant to be an opportunity to thank a performer after watching their performance. If you are going to be an autograph hunter, see the show at the least."
I rarely stage door. But on the rare occasions when I do, I often go to a different performance to do it... since it is nice showing up 10 minutes before the audience lets out and getting a nice spot. I usually bring my ticket stub to show security, if they get persnickety. And I've never stagedoored a show I didn't see... well, OK, that isn't entirely true. I often stagedoor a Broadway show a friend is in, if I'm walking by when his show is letting out. I noticed he signs before he looks up at the person, so I've put Playbills for Hedwig, Something Rotten, and a few others in front of him, just to mess with him. But that doesn't really count. 