On 90210, Season 1 DVD, on the 4th episode of the 4th disc, the episode where the gang goes to Palm Springs (I believe it's called "Palm Springs Fling"), when Kelly, Donna, David and Steve first arrive to David Grandparent's house, they pass by a pillar in the the livingroom with a large mirror on it, and as the pass you can see what I assume is a crew member in the reflection of the mirror.