You know she doesn't care much about you, so it's useless for you to express yourself in a hurry; First, you should make her notice you, and then make her like you. It will take some time, and when her relationship with your friend reaches a certain level, you can express yourself directly.

Boys should be brave. Personally, I suggest that you don't confess to her on your signature. You'd better say it directly, in person.

I wish you success, come on ~ ~!