Towards the beginning of the movie, Brad and Janet are approaching the mansion in a rainstorm, and a pennon can be seen flying from the mansion's roof.

Sadly, my copy of the video is getting very worn, but I think the design is a white pennon with a black circle, on which is a white lightning bolt. A similar emblem appears one Riff-Raff's costume towards the end of the movie.

Presumably, this is the flag of the planet Transsexual, in the galaxy of Transylvania (not to be confused with the central European region or Transylvania!)
James Dignan, 27 May 2004