Stoke was one of the first signalling schemes to use axle counters on a widespread basis. One of the concerns was that in the event of an incident staff would not be able to halt trains on other lines quickly using a track circuit clip. So signs were put up giving the direct number of the relevant signaller so they could stop traffic quickly. I presume with the introduction of GSM-R and its emergency red button that would be used instead, and the signs are now redundant.