[OSM-newbies] Proper use of "bicycle = no" tag

[Isaac Wingfield]

I came across a place today where there was effectively a  
"sidewalk" (paved, smooth, wide enough for two-way traffic) about a  
hundred feet long, connecting two dead-end streets. There was a sign  
at the end saying "NO Bicycles. NO Skateboards, ..." basically  
forbidding everything that has wheels.

It occurred to me that there could be two entirely different reasons  
for using the tag "Bicycle = no"; first, because of the condition of  
the surface, or its slope, or something else physical, that would just  
make it impossible to ride a bike on it, or second, that although the  
surface would be fine for bike riding, it is forbidden by a sign.

So the question is, does that one tag "bicycle = no" apply to both of  
those cases, or is there a proper tag for the way that would make the  
difference clear?

Isaac