I have a level of heightened alertness around police officers with guns and soldiers with guns. That tends to lessen my level of comfort. It's the guns that make the difference, but the degree of difference depends on the context.
For example:
1. Cops on duty, in uniform, drinking coffee = Mura noticing, observing, checking what/who else is around, deciding whether the cops are relaxed or not, and choosing a comfortable safe distance from said cops in which I can relax too. Note: This level of uncomfortable awareness will not stop me talking to said cops in a friendly manner if I want something from them, like directions.
2. Cops on duty, in uniform, hands on holsters = Mura on instant alert and making use of the nearest exit immediately.
3. Soldiers in uniform, holding rifles (or whatever the hell it is they hold), patrolling around a political event, embassy, airport, or other high security setting = Mura persuading herself this is a necessary evil while seeking to leave the area as quickly as possible.
4. Soldiers in said situation who make an effort to communicate that things are fine and that I can relax = Mura smiling at said soldiers and seeking to exit scene slightly more subtly.
5. Soldiers or police in dress uniform on parade duty = Mura relaxed even if the guns are real.
6. Cops out of uniform but with guns visible, in a car = Mura checking out said car for hints that it is a police vehicle, and then moving away from it.
7. Cop out of uniform, not obviously on duty, with unusual gun gear visible = Mura obsessively studying said person for signals he/she is a cop and not a homicidal maniac while desiring very very very much to be as far away from said person as possible. (Real life example: The time I was sitting on the J train in NYC and noticed the guy sitting on the bench opposite me had a pistol in an ankle holster on his leg, visible when his trouser leg rode up as he sat down. I spent the whole of a 45-minute trip trying to judge whether his, lean, tight, but middle-aged physique, extremely polished partially bald head, and superbly neat moustache were NYPD regulation or sign of a psycho. I sort of concluded he was a cop, but I still wasn't satisfied entirely, and I could hardly wait to get him out of my sight.)
8. Anyone who doesn't look like a cop but is clearly armed = Mura concludes this person is or soon will be a criminal and seeks to get far away asap.
9. Anyone who looks a whole lot like a cop or soldier but turns out not to be either = Mura doesn't wait to see if they're armed; she scrams.
What all that boils down to is this: Guns make me nervous. I don't like them. They are noisy, nasty, dangerous things that have no peaceful or friendly connotations. I don't like to be around them, and having them around injects an note of tension into any situation.
However, people also make me nervous, some more than others. When you add the two together, the nervousness factor ratchets up significantly. For instance, I may not like the idea of a gun lying on the table in a room I'm in, but I'd like the idea of someone holding that gun in that room even less, because it is the person holding the gun that is the wild card factor.
If the unpredictable, uncontrollable person holding the gun is a qualified professional on legitimate duty, my nervousness reaches a certain level. If the unpredictable, uncontrollable person is just some random stranger off the street whom I have no reason to believe is not some kind of wacko or moron, then my nervousness is magnified exponentially.
But even this is not a set in stone formula. There are always things like this:
Link. So much for trained professionals lowering my nervousness around guns.