The JM stamp is found on the left (port) side of the barrel at the point where the barrel meets the receiver. The Rem-lins have a REM stamp on the right (starboard) side of the barrel, again, just above where the barrel meets the receiver. The JM marks a weapon built by the old , veteran Marlin team—the ones who built quality weapons before Remington bought the company and fired the ones who new what they were doing.
The Remlins were built by inexperienced personnel so the quality suffered. At present, therefore, a wise man will look for a JM-stamped Marlin, and be willing to pay a premium for its quality. If one does purchase a REM-stamped rifle, one will examine very, very carefully to be sure the stock's fit and finish are good, that the barrel is straight and has the sights properly aligned. I had the opportunity of comparing a new JM with a new REM Marlin last year. Both were on the rack at my local Gander Mountain. Even I, a rookie in the Marlin camp—and to shooting, really, could see the difference between the two pieces. The JM was clearly a superior product.
Given another two years, Remington may be able to make a quality weapon. We are beginning to see reports of good weapons, already. But the good ones are too rare to think that Remlins are equal to Marlins, at least not yet.