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).
There’s a couple near me. 1 on an arched footbridge, on a busy pedestrian path. The other on a narrow, cut through. It’s near a school and people turn into it around a blind corner.
I consider both completely reasonable things to ask.