The wiki page here (http://wiki.openstreetmap.org/wiki/Key:bicycle) redirects to a rather elaborate page that explains how to set the various bicycle-related keys for cities.
However, I am mostly interested in riding outside cities; so the only applicable guidelines are (taken from http://wiki.openstreetmap.org/wiki/Bicycle)):
bicycle=yes: Where bicycles are permitted, overriding default access…
bicycle=no: Where bicycles are not permitted, ensure this is indicated
I guess in nature, the default is that bicycles are permitted, so “bicycle=yes” seems meaningless. However, I have seen that key set for quite a bit of ways (http://overpass-turbo.eu/s/8sb), and I wonder whether it has some meaning, or (if it doesn’t) can be given a meaning.
Perhaps, we should mark a trail with “bicycle=yes” if it is used for cycling, but not enough for “bicycle=designated”?
Maybe, we should mark “bicycle=yes” when a trail is passable by bicycle, but we cannot be more specific with e.g. “mtb:scale=2”?
Right now, my opinion is that we should never use “bicycle=yes”, but there is no point in removing it where it already exists. I am not satisfied by this resolution. Please help me by expressing your opinion.