There may be many reasons for a boyfriend to delete his personalized signature, and the specific reason may be to ask him himself. But I can provide some possible explanations:

1. He may want to change his image, and deleting his signature is part of it.

He may think that his previous signature is a little naive or immature, so he decided to change it.

3. If the signature is about you or your feelings, then he may want to reduce the openness of feelings by deleting it to protect your privacy.

He may encounter some problems, and deleting his signature is his way to deal with these problems.

These are just some possible explanations. The specific reasons need you to communicate with him and understand his real thoughts. Please remember that everyone has his own way of dealing with things, so it is best to ask him with an open and understanding attitude and listen to his answers.