For me it's a weird mixture of both. If I see armed police where there wouldn't normally be any I straight away assume that maybe they expect something to happen, maybe they've received a tip off, and that scares me because however many armed police there are, they might not be able to stop all kinds of attack (if it's a response to a possible terrorism situation for example), and I wouldn't have all those thoughts if I didn't see them. But on the other hand I think that having their presence would put off other potential criminals, and might make the chances of a general crazy person attacking far less likely so I suppose I feel safer in that respect.
Anyway there wasn't an option for both, and I couldn't bring myself to say I sniff bumholes
... so I went with 'feel scared' because I probably lean more towards that. I tend to live in my own world most of the time and when I'm out and about I don't usually consider that something really bad might happen, and armed police (as much as they're doing a great job) tend to crush that world a bit