An "RE" serial number prefix is factory code for:
R - Denotes standard size frame as opposed to a Featherweight or "FW" frame;
E - Denotes that this gun was originally shipped with optional automatic ejectors.
With the exception of the "R", "FW" and "E" prefix symbols, not other factory code prefix stamps are included with Smith serial numbers until the company is acquired by Marlin. Marlin only produced Smith guns on the featherweight frame, but these later guns also feature another prefix stamp "S" to denote the gun was produced under Marlin ownership; therefore all Marlin era guns are prefix stamped "FWS", and Marlin era guns with auto ejectors "FWSE".