On the cover of the GJ, if you look closely at the medallion of Vanitas, you can see that the medallion holds in skeleton arms. These hands are also on other illustrations and not only. Maybe you remember post by @eglantiney about VnC cover art. She mentioned the pair of hands that being held the watch on the special thanks page and she noticed the frame on the keychain with Noe which also has hands that hold the skull.
Then cover of vol.3. A small skull on the top of the frame is also in someone’s hands. And the small frame around it a little bit like Noe’s frame on the cover of the vol.2.
As for the medallion of Noe, there are feathers, which we have already seen! On color illustration to the 11th chapter and on the bonus card to vol.2 Noe had a decoration with a feather + Teacher’s adornment has a feather too.
What letters on medallions? I looked in Gothic script and..
it’s look like the
medallion of Vanitas
has a letter I or maybe J and the medallion of Noe has G. I have no idea what those letters mean and whether it’s letters at all. But if it really is letters, then I think that maybe these are the first letters in the true names of Vanitas and Noe.