I don’t think that it is very common for an employer to notify non-affected employees when someone is terminated. HR, direct management, and security are normally notified of the termination, but not necessarily the reason (well, except for HR, who obviously knows why). It sort of looks bad when a company has to fire someone, so, I think that they try to keep it under wraps. Also, regarding the two-weeks-notice issue, it’s pretty common for them to have you leave the premises upon giving your notice. The lucky ones get to pack their own boxes, but that is not always the case. It’s why you want to have all of your stuff out of there before you actually give the notice. Back-up and/or remove whatever you are lawfully allowed to, and then give your notice. I wouldn’t leave anything there that is fragile or extremely personal, though, as – again – you may not be the one packin’ the box. Employers often pay you for the specified period (i.e., two weeks or whatever), but in their eyes, you went from “loyal employee” to “rogue operative” or “employer terrorist.” So, they may want you out of there before you can do any damage.
As far as carrying at work, even if it’s not in the handbook, the employer may still be able to fire you. It’s their employee-at-will protection. They still have rules to follow, but, it will probably be a safety issue. The weapon may cause alarm and concern among your co-workers. No doubt that the employer can find one or two of them that will testify or sign a statement saying that, at some time during your employment at that organization, you made some kind of gesture or comment that could now be construed as hostile or violent. And given that potential terrorists list – it could even be because you are a veteran.