Yes, I call out, but it seems it has to be done at the exact right time: If I call out too early (happened once or twice), a surprised rider may nervously jerk his head to the side/rear, so I try not to startle anyone. If I get the sense that I may alarm them, I'll refrain, at least until they have noticed me, visually.
If a rider passes me, I am more dis-appointed than anything else: (I just wish she could have said hi before she dusted my broom). I always look for the cameraderie in anything I do.