3d2y

Luffy's way of saying ; we will meet in 2 years not 3 days ;

There is cut on 3d and 2y is normally written
it is there on his arm as a tatto

its writtten like 3

d

2

y

on his arm

there's actually no sentence but ; he did it by fake intrusion in marine ford then one purpose showing his arm (with 3d2y)
to tell his nakama ( crew ) that we'll meet in 2 years