Barney Martin had two different guest roles on the series. Once as Tom Hanson's, Johnny Depp, partner in 21 Jump Street: Pilot (1987), and once playing an alleged kidnapper in 21 Jump Street: In the Custody of a Clown (1987).
Officer Judy Hoffs:
How many times have you seen this?
Off. Tom Hanson #2: 122 times... but I don't watch the whole tape. I watch 3.3 seconds. 3.3 seconds that slipped through my fingers. 3.3 seconds where I could've done a thousand different things. But I didn't move. Do you know how many...
Throughout out the series, it's clear that the actors/actresses portraying teenagers are actually in their 20s+. This is done as to not interfere with the schooling of real teenagers and to give the general viewing audience who are teenagers themselves someone they can look up to.
In the DVD releases by Anchor Bay Entertainment, most of the music is replaced with generic music due to licensing issues.