In Norway there is no equivalent to "On your left!", and I have never heard anything called out to anyone. The only similar thing is "Hold right!" called out in races, and that's often considered a bit aggressive, a.k.a "stop weaving all over the place, you moron!"

Personally on busy roads and paths I ride as if I'm about to be passed all the time by anyone, and I try to always pass other people with plenty of clearance. If they look like they're paying attention (holding a straight line, moving fast, checking their backs) I do pass closer than I do someone who seems oblivious or jumpy, but never as close as inches. If I have to squeeze by someone who's not paying attention I have to think of something to call out, at the moment it's, in a singsong voice, "I'm passing you, on the LEFT-hand side..."...