Why do they keep showing us shots of the detectives unloading their guns and putting them in their desk drawers? I think they're lining us up for an accident or a dramatic climax involving a Police weapon.
I wouldn't swear to it, but it's just a quotidian thing - sort of like hanging a coat up when you come in.
I'm fairly certain I've seen it in prior series, and I think, were they not to do it, the sort of people who spot continuity mistakes, and errors in basic procedure would email the producers, tiresomely. I could be wrong though.