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).
I think the crossing I'm thinking of might be at a 30 degree angle or so, so that might be the logic there. But in that case: Caution Angled Railway would be more likely to result in actual caution instead of contempt.
I do remember a sign of bike crashes someone made for a city and all the hotspots were angled railway crossings.