This is a Coinbase wallet.
I used their "sign message" ability.
Let's try a one-liner: (No linebreaks,whitespaces)
This is the real atp1916. Date is 09/18/2016.
HNFsWXXz85Q+dmwaSLPDkpgqv+N3dRO+9FLWUnit8KyjN2vVAOExybus82bg8HBoe5ND1LUXK8ATcF4V2dHBaLw=
The address was posted long enough ago for me to believe the this account either belongs to you or was sold with the original private key.