I think it's the mintmark. Actually, I'm surprised that NGC even attributes it. Several years ago, I submitted four of the Accented Hair Kennedys for attribution to include a DDO that was listed in the CPG. When they came back without the DDO, I resubmitted them for review and was told that the doubling was too minor to attribute. In my opinion, you could see it better with the naked eye than you could the DDO on this nickel. Chris
According to doubledie.com and a few other reference websites it's seen on the motto and the date I want to share this picture from the doubleddie.com website -
I will find it when I return home. But here is the NGC info I want to share this website with you - http://www.ngccoin.com/coin-varieties/jefferson-nickels/2004-p-handshake-5c-ddo-fs-101-1597/
Thanks to all of the above, I was not even aware that there was a 2004 DDO. The Cherry picker's volumes, are woefully far short on many post 1990 strikes. Again thanks