The "X" on Luffy

While all this talk about 1138 and 1139 is goin on... I'm here still confused by this. Could this be a connection to JoyBoy? It isn't the friendship tattoo from alabasta coz: 1. It wouldn't be so clear in the picture 2. It has already washed off long ago

I honestly don't know what to think, I wanna hear your guy's thoughts.

Also this is my first post but I've been theorizing for years now, so I hope you can welcome me in!