In the top left corner you see some gibberish letters. That's a Trip Code. When someone makes a post on 8kun, they can enter a name and a passphrase. If you enter the same passphrase you get the same Trip Code. But it's nearly impossible to start at the Trip Code and figure out which passphrase created it. (You can go forward pretty easily, but it's almost impossible to go backwards.)

So when a poster like Q wants to show everyone that they're the same creator of a previous post, they enter the same Trip Code passphrase.

Over the past few years Q has used one trip code for a while, and then cycled to another one. So if he's using code A for a while, he might post with new code B saying "this is me now" and then he uses A to say "confirmed, I'm going to be using B now"