Naming bridges by number is a recent thing, in the past they were either called by the approx. milepost location (103 bridge Hall, etc) or if they were close to a prominent landmark like a street (Met at Jay for Metropolitan Ave) or something nearby, like the Meathouse at Hall. If it was the start of an interlocking, then it would've been the West Bridge Babylon, etc. This would have been something that was consistent and taught as such for the physical characteristics in training. Over time the policy has changed as naming specific locations or signals in train orders could be painful, so when they went from the Form 19 to the Form L and changed from a C-Card to Rule 241 for passing stop signals, they now name all signal bridges and interlocking signals with a sign.
As for that specific location at that time in Babylon, it is well ahead of my time and I wouldn't know, besides maybe to refer to the Emery maps, or someone else's PC maps from that era. Back then if the signals had a id plate with a letter with S ##, then it was an automatic (as opposed to an interlocking signal) signal, with the letter indicating the branch and the ## the milepost location to a tenth of a mile. If it was odd, it was westward, even - east. It was possible for a bridge to have a mix of automatics and interlocking signals, especially back then when there was more Rule 251 and 409 territory. In the map under the pic, the sigs for the Central branch would be prefaced with a C, not an S.