Do the MAKI letters even do anything?

[Woody Alien]

Sure it's nice and fun to go search for them in the levels among other items (I'm missing the 6th and last necklace btw), but is there any purpose for them? There's not even an achievement for that unless it's part of the quests somehow. They have a prominent space in the inventory menu but they seem to be just collectibles and nothing else. Currently I'm missing two of them in the overworld, but there should be at least a reward for finding them.

[HunterN]

Nope, definitely seems like a missed opportunity to not at least have an achievement. Maybe another cute largely cosmetic reward like the pirate ship too.