I see these every time a bicycle path intersects with any kind of car or train infrastructure. It just seems really patronizing, as if we’re not capable of slowing down without getting off the bike; it also shifts responsibility onto the cyclists if there is a crash based on something arbitrary (mounted vs dismounted).
You are one of those guys who race full speed through the pedestrian zone then? Because that’s where those signs usually stand, to be ignored by nearly all bikers.