I've found a bell works great if done in advance. People often glance back and see you coming, then stay right. As far as verbal, it should stay as "on your left". Changing it up makes it harder to educate those not knowing what that means. After they're used to it the just move right automatically. But not everyone is out there all the time. It's the once in a blue moon types that are more of a risk. Everybody has a right to be out there. Be respectful, safe, and slow down as needed-usually no issues that way.