From time to time, you will catch a Pokémon that has a certain mark on it. This mark acts like a Ribbon in that it appears in the status screen when your Pokémon achieves a certain thing, most of which are determined on capture.

The Mark Rarity is as follows:

The Mark Charm was introduced in Pokémon Sword & Shield's Isle of Armor. This basically gives 2 extra rolls for getting a mark, essentially tripling the rates.