St.'s an abbreviation for Street Saint (although in British English the trailing period's commonly dropped, that's, as "St" rather than "St.") The usage's understood by context. For example, the expression "St. Peter St." would be assumed to mean "Saint Peter Street". Ste.'s the abbreviation for the French "Sainte", the feminine form of "Saint", commonly seen in English references, for example Sault Ste. Marie.… (More on St)