When riding with my son on trails I always have him ding the little soccer ball bell I put on his bike. Its loud for its size and works well. When I'm alone I just say left. Also be alert on sweeping curves that have trees, people like to ride two abreast and fail to fall inline on the curve and the person on the left is suddenly riding right at you on your right lane from behind the trees that blocked their angled approach.

With that said, I'm a runner first and most runners do what I do and wear an ipod. So I always caution my son and use more caution myself when catching up to them because if they are wearing earbuds that seal your ear canals they can't ear much at all. I wear the stock Apple ones because although the new style is more sealed they still allow sound in and I feel like that's important to hear cars especially.

Once on a ride with my ex we caught a longed hair woman wearing shiny sparkled yoga tights. She says look at those crazy tights. (This because I'm obsessed with yoga pants and make my gfs wear those and running/volleyball shorts lol). Anyway, we get closer and I see back hair because the shirt must have been from Baby Gap. I say that's a dude! We pass and his bike though a C'dale looked like my Trek. So I say nice bike dude as I'm beside him and he looks at me and says thanks with full eye shadow, blush, red lipstick. Not the most shocking thing I've seen, but the talk of that days ride. Too each their own.