I bought a 1968 S penny while scanning the EBAY the other night and got it today. It's looks like Double Die. Maybe it is just the so-called over strike variety? thanks for the help.
Mechanical doubling. Notice: 1) It is flat and shelf-like, as if part of the design was flattened. 2) Affects both the mintmark and the date in the same direction. Since the mintmark is added to the working die after it has been hubbed, the doubling you see on both the MM and date cannot be caused by a doubled die. 3) The doubling "takes away" from the design, rather than adds to it. By that I mean, if you take away the doubled part of the date and mintmark, the designs would appear smaller than a normal coin. A doubled die, since it is an additional hubbing of the working die, will result in an additional set of raised letters/digits on a coin. They will "add" to the design, because they are a second hubbing. Considering all this, all signs point to MD. I have a nice tutorial about the main types of doubling that you can see here: http://www.cointalk.com/threads/lets-talk-doubling.224087/ Keep up the hunt!
MD is much more common than a doubled die (especially from 1968-1972), and much less collected. I personally wouldn't pay a premium for it, but someone else might.
usually no added value for MD, some even consider it damage, heres another good read.. http://www.ebay.com/gds/How-to-spot-a-fake-Doubled-Die-/10000000017558006/g.html
