Unobservant fan is unobservant
Okay, I was watching a rerun of an episode of Numb3rs... and suddenly noticed that David Sinclair was firing his gun with his left hand. And taking notes with his left hand. Etcetera.
A quick check of a couple other episodes confirms that he is, in fact, entirely left-handed.
I'm very embarrassed that I never actually noticed! *facepalm*