It is interesting that police had the frequencies and permission to use them ... and a shame that they have now been told not to.
I've seen the call numbers at many intersections. Tags wrapped around poles where the sign is no more obstructing the view than the pole. But I'm not sure the general public would see it or call it.
I'd like to see pull boxes at major crossings where a police officer could signal a problem directly to the railroad ... perhaps even keyed if the railroad is afraid of misuse. (Many buildings have fire department lock boxes on them where the fire department can access keys to the building if needed.) It would be one more thing to maintain.
I've been listening to a local railroad deal with false activations, partial activations and broken gates at their crossings. Being able to clearly communicate a problem in advance to trains is not a bad thing.