Standard practice around here is for bikers to shout "On your Left!" or right as the case might be. Most bikers in the conservation area do that (maybe 60% of the time).
HAH! Double HAH! I've tried the "on your left" thing, and barring two cyclists, and one guy carrying a kayak, it provokes one of three reactions: they pretend not to hear, they get mad, or best of all, they think it means "Jump to your Left"! Really, the bell option works best, if you have the right bell. Mine is a little single dinger. Not loud, but so unusual the peds hear, look, and smile - usually.
Where I ride, the trails are multiple use, meaning bikes, peds, dogs, and horses. None of them are predictible, least of all toddlers with training wheels who are trained to perform as Roger seeking missiles. It simply isn't possible to go full bore on a twisty trail and limited sight distance. On the other hand, it isn't really necessary for three people on foot to occupy a section of trail 15' wide. Nor do a half dozen need to congregate on the approaches to the foot bridges.
You say there are foot paths only for walkers. You need a wee bit of enforcement up there. Here, we have occasional bike police, members of the police department, I mean. Not often enough because it's not often a major crime area, though.