A schoolmaster I had in the 1950s, who taught Latin together with Religious Instruction and was himself an ordained priest of Anglo-Catholic persuasion, would always insist on writing the abbreviation for saint as S.
Moreover he demanded it from his pupils so that St Paul had to be S.Paul etc. His argument was that he did not want them to be confused with streets. However street is most often abbreviated Str.
This was not his only eccentricity. He had many oddnesses, not least when supervising rugby, when he would often robustly join in the action.
Since I never met anyone, before or since, who abbreviated saint in that way, I am wondering if anyone else ever encountered it?