It is indeed a Murray frame. JC Higgins is the most common badging you'd see. The Murray guide that Wildcat linked to is incorrect information that made the rounds a few years back. It's about 6 or 7 years off if I remember correctly. Also, the important letter in dating your frame is the L in MOS-L. That stands for Murray of Ohio Supply. The MOD number is the model number for use in order forms.
Despite this, the year he gave ended up being accurate to my lists with 1947. An interesting thing to note is the dropouts, which are that of the transition period frames from the very early postwar period, being changed to Schwinn style dropouts very soon after. Seeing this corrects my list and suggests that they did indeed include 'I' in their stamping (which some companies left out to avoid being mistaken for the number 1), pushing everything back a year and making L 1946. It'd be on the early end, too. This also means it could have possibly been badged Elgin, which was around for only a blink after the war.
That all being said, it doesn't have much special significance other than intriguing to people who are interested in company history and early postwar production like I am. It's a case of uncommon but not valuable. Truss rods are original and fork appears to be as well, so that's nice. Looks good as it is though! Enjoy.
