u/EqualInteraction5689

What is this weird spot on my mouthpiece it doesn’t go away when I clean it?

Basically, I play tenor and I recently got the one I’m gonna be renting from my school over the summer. It came with an extra mouthpiece, so I decided on to clean them both but the one that says Yamaha on it is my main one(and it’s had this spot for a couple days other for reference) I just cleaned them both and it’s not coming off? What is it?