I would ofcourse say ‘No’ but I would be concerned about how the uniformed person could potentially react. I think it would be a combination of the ‘officer’s’ failure to identify him/herself, my inability to identify his/her uniform and the no introduction, direct question ‘do you have a gun’. As a foreign visitor I would not be aware of what the protocols are, what the ‘officer’ should do, what his powers are, what I should do etc. I also think that it is a cultural thing. I am just not used to seeing police officers carrying weapons. It is still quite unusual here and ofcourse we have very different gun laws. For some reason ( maybe Hollywood?), I have no fear of British police but I am wary of US police (maybe that is a good thing from a law enforcement standpoint?). I think maybe that British police do a lot more than ‘law enforcement’ and are more involved in local communities.
British police do come under scrutiny for things like Hillsborough and political/celebrity sexual abuse investigations etc but it is rare to hear of innocent citizens being shot. I think that they are portrayed by the British film and television industry differently. Also police here wear an easily identifiable uniform and if not in uniform would immediately show their badge for inspection. That offers me some comfort.
If anyone is to blame for my perception of US police, I would lay the blame at Hollywood’s door rather than the news media.
Anyway, if during my next holiday to the US, a person in uniform approaches me and asks ‘do you have a gun?’ at least now, thanks to the OP and others, I know how to react.