in all countries I visit, I prefer following tactics "first ask, then shoot". Although I mostly prefer nature photography, which also has less restrictions :-D (did not encounter a deer complaining about taking a photo of him :-D ), on holiday I also shoot in cities etc.
For example, I was positively surprised, that in Moscow (Russia), where I expected more strict rules, after asking a security guard in GUM store (some my photos are here), he answered, that it is allowed to take photos there (while in similar stores in Czech Republic, taking photos is mostly prohibited). As I wanted to take a photo of one beautiful metro station in Moscow, I asked a nearby policeman. He said (with smile) something like "Ok, take quickly a photo and go.".
I also think, that it is a good idea to prevent taking photos of places with too many people in uniforms (like police stations etc.). But for example, as we visited Israel, things were quite different. Our colleagues asked some armed soldiers patrolling on a square, whether they can have a photo together with them - no problem! Taking photos in Jerusalem - streets, market places etc. also no problem (avoided obvious taking photos of particular people). The same in Bethlehem (same guidelines).