if you are in your boxes and arrow over to the Memories page, it will normally say that the pokémon has no marks or ribbons, but sometimes it won't and will instead have a “Title” thing at the bottom (look at the Mystery Gift Pikachu for an example)

that means the pokémon has a mark (or ribbon)! you can only select these from your party, NOT the boxes, so move it out of the boxes into your party and then close the box view and go back to that page

(there is a slim chance of a pokémon having a mark when you catch it, and they can gain them via certain events. they are NOT selected by default; you have to manually select them)