User blog comment:Ryuske/Luffy's tattoo/@comment-1595565-20100806010429

It is most likely a date to meet back on sabaody. If the last two symbols mean "calendar," then the first two could indicate the date itself. It could be saying something like "fifth day of the tenth calendar month." I'm just simply guessing here, but it could be a date, maybe even a time, assuming that the stuff above is even remotely correct.