@OZ1972
My June 8th post quoted above may have been taken out of context of a 1953 Western Auto Western Flyer X-53 bicycle example; (i.e., not Sears (S)).
For a 1953 Sears bike the serial number might be prefixed by a “MOS-S”.
Your “MOS-R” reflects one letter and one year prior, 1952.
“MOS” was not for “Murray Ohio Supply” but rather for “Murray Ohio—Sears”.
It gets even more interesting when Murray moved to Tennessee in 1956, when they used “MOTS-V” for 1956 “Murray Ohio—Tennessee—Sears” or perhaps “Murray Of Tennessee—Sears”.
Your bike looks green.