wtf

Seriously WTF? Okay, it's a reference to an episode of One Piece where the crew tied bandanas around their arms to identify them in case on of them was mimicked by a certain foe. However, they also put an X under the bandana as an added level of identification. Brilliant!

BTW, does that say "Alchemist" in the sky there?

I think it's supposed to, but the artist got the pronunciation wrong.

Thought so. He must have got hung up on the "ch" and used チ instead of ケ.