Why does Ace's tattoo on his right arm say "Asce"? Why does Ace's right arm have "Asce" written with the "s" crossed over?
It's Sabo's Jolly Roger.


  Ace had another tattoo on his upper left bicep that spells "ASCE" vertically. The "S" crossed out is a tribute to Sabo as that's his jolly roger. 


(Source: Portgas D. Ace on One Piece Wiki)