Is there any letter on the comb?

Yes! I believe it was spanish and Arthur has seen it clearly despite telling Marina he couldn't. The "You know that I love you".

I mean the letters were in between the flowery design on the comb, can try zoom in a lil bit

went back to the chapter and saw the letters.. would never notice them they blend in so well.. now i feel bad for nox #－.－)

It should be latin: Tu scis quia amo te

Correct babe, I just typed in the literal translation of the beautiful phrase in english instead