It is interesting that you use the name Dan Martinez. Leon Martinez has made similar belts and uses an LM, however I have no idea if Dan is any relationship to Leon. The turquoise looks like it could be Morenci, if you see quartz call it Kingman. It is very possible the belt is from the 1970s, and if you feel like the seller has no reason to deceive you I would go with it. From the image it doesn’t look new. I couldn’t find anything in the hallmark books for the DM.