If you are lookinfg for the gallery, see Mossberg HS12 Gallery.
Upon meeting two strangers called Dave and Tony in an abandoned bar in Season 2 Episode 8, Nebraska, the man named Tony (Aaron Munoz) can be seen carrying this over/under tactical shotgun with the stock sawed-off and possibly the barrel too. He fires it one time into the ceiling when Rick is forced to shoot him three times. Rick Grimes (Andrew Lincoln) fires the shotgun twice at oncoming walkers in Season 2 Episode 9, Triggerfinger, before running out of shells but they do bring the shotgun back to the farm later on in the episode and possinly add it to Rick's bag of guns.