Your girlfriend broke up with you a week ago and changed her signature to "12day". This may mean that she is experiencing some emotional difficulties or has some special emotional associations. However, it may be difficult to directly interpret the specific meaning of this string of characters, because it may be just a way for her to express her feelings, not a specific instruction.

In this case, the best way may be to communicate with her directly and ask her about her recent emotional state and the specific meaning of this "12day" signature. Maybe she just wants some space and time to deal with her emotions, or this number has special significance to her. Only she can accurately explain the meaning of this signature.