vwvortex's Mk3 forum defines a show car as one that has at least 3 of the following:
-Smoothed rocker panels
-Colormatched/Fully polished BBS RS wheels
-Pulled wheel arches
-A shaved/smoothed engine bay
-A cocky, self-promoting, and 'holier than thou' owner. (this quality is pretty much required)
If the car is at a show, but driven off site before being loaded onto a trailer, it is considered a daily driven show car. Also, if the owner insists that he doesn't lower it farther than it's normal height for shows, he does.
"Damn, look how low his car is! The painted lip is ABS plastic, and has no scrapes on the bottom of it. This must be a show car!"