When Tim is talking to Charlie Hill (Terry-Thomas) about Julian Buck's son, Charlie tells Tim, Julian's son, Thomas, was raised in Austria. In fact, the actor who played Thomas, Karlheinz Böhm (as Karl Boehm), was a native Austrian.
One of the portraits on Thomas' (Karlheinz Böhm (as Karl Boehm) office wall is native Austrian actress Romy Schneider. It is an In-Joke to native Austrians as Karlheinz Böhm and Romy Schneider played girlfriend and boyfriend or husband and wife several times in Austrian films, Austrian television shows and at the Theater in Vienna.
Ed Begley, Karlheinz Böhm, Corinne Calvet, Rita Moreno, Terry-Thomas and Keenan Wynn all receive 'Special Guest Stars In Alphabetical Order' credits.
The movie being shown at the drive-in in the opening scene is Stagecoach (1939). Interestingly, it is being projected in the wrong aspect ratio (1.85 instead of the correct 1.37).
The series' producer, Aaron Spelling, himself a former actor, appears briefly in the surveillance footage as the man lighting a cigarette.