On rail trails I ring my bell, or verbally announce (usually "On your left"). I have had very positive responses to the bell by pedestrians if rang well in advance... I often have people thanking me, and they get over to the right side of the trail.
When I am riding with friends, as I am beside the peds or slower cyclists I will usually say something like, "Two more coming."
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Slow Ride Cyclists of NEPA
People do not seem to realize that their opinion of the world is also a confession of character.
- Ralph Waldo Emerson