The PrincessRBN is a hint towards Transfem Ralsei.
The other ribbons so far are pink, white and blue, that's literally how they're described
all of those have strong associations with Ralsei, in part due to the game putting them on her (check a fresh ch2 save for that) and in part due to the very elaborate reactions she has towards them (the Blue Ribbon has SIXTEEN UNIQUE PIECES of equip text)
On that last note, the Twin Ribbon's description states "you'll have to tie your hair in pigtails", and Ralsei's reaction to it is "try around my horns!"
Onto the Princess Ribbon itself, we still don't know about a single PRINCESS in utdr. The closest there is is Mettaton in that one sce- wait fuck
TANGENT: METTATON'S DRESS
Mettaton is the closest to a princess in utdr and he wears a dress almost identical to the one on the Mannequin
Ralsei says the mannequin's dress is cute
There is also another Mannequin in hometown, dressed up as Ralsei.
Ralsei's equip text for the item is "Cute! (Gloves don't fit)". She wears something that is definitely a symbol of femininity, while saying it doesn't fully fit her.
Ralsei is implied to be amorphous. She turns into a pile of fluff, her face changes when she takes off her hat, and she can fit in a whole horse costume by herself
If Ralsei can change shape, why wouldn't she be able to put on the gloves????
I'm not saying Ralsei is definitely transfem because of a few ribbons, I'm just saying she's repeatedly being shown to embrace symbols of femininity even if they don't fully fit her. The supposed Prince of the Dark, as foretold by fate itself, puts on literal princess's clothing even when it doesn't fully fit her.
I have further thoughts about the prophecy and how it relates to this (long story short Ralsei isn't alone in the dark so why would she still be required to be a prince) but that's beyond the scope of this post and my hands already hurt somehow
