My girlfriend and I just sat through all 2.5 seasons of The Walking Dead. For some reason, she was rather tolerant of my need to point out all the firearms errors throughout the show. The aforementioned safety on a Glock was pretty bad, but there are others. Shane tells Andrea that her S&W 3919 has a seven round capacity. Glock mags are all 10-rounders, and at one point we see a 10-rounder for a Beretta 92FS. There's an M4 with no rear sight (and the guy using it makes a long shot with it).
Likewise, everyone on the show demonstrates a remarkable proficiency with firearms even with very little training, beyond Rick and Shane, anyway. Still a fun show for all its foibles, and to their credit, they did get it right in the scene in Season One where Andrea pulls her 3913 on Rick with the safety on.