1) It is doubleD die; 2) The mintmark is punched separately. 3) then the MM would be a re-punched MM. 4) Pix too blurry to tell
I checked and there are no doubled die obverse listings for 1979-D. If there were any someone would have found it by now. There are some RPM's listed though. If the mintmark, and date are doubled that is proof of worthless Machine doubling. I toss all the 1974, 75, 76, 77, 78, and 79's into the Coinstar box. I think the design is pretty ugly anyway. If it is a RPM it's not worth very much.