Post-1913 frames are usually marked with a 'R' (Regular frame) or 'FW' (Featherweight frame) BEFORE the serial number; if followed by an 'E' the gun is fitted with ejectors.
A Field and a Specialty
An 'R' AFTER the serial number is found on guns c. 1910 - 1920 and believed to indicate an extractor rather than ejectors.
An Ideal and a Specialty
Marlin era (1945-1950) guns are prefix stamped 'FWS' if extractor and 'FWSE' if fitted with ejectors. Some are simply stamped 'S' and some 'FWM'.