Welcome Rob, it is a classic shelf type MD. Very common on late 60's coins, when you see it on both mm and date in same direction of movement, it's 98% of the time MD...there are certain date/mm where there's a
DDO AND RPM on the coin, not that often and on known coins. Check those question coins against reference sites:
www.coppercoins.com
www.doubleddie.com
www.variety vista.com