Ex never signed birth certificate but went to try to get one for my son fond out they would not give it to him he then signed my name to have birth certificate changed to add his name

Where? Is there proof he's the father, a DNA test?

He certainly committed forgery under "most" circumstances. I just don't know how serious it is.

I assume you want the name changed back?

Ex never signed birth certificate but went to try to get one for my son fond out they would not give it to him he then signed my name to have birth certificate changed to add his name

I don't believe it.

A birth certificate cannot be changed, so as to add the name of a man as the father, simply upon the signature of the mother.

As a legal document, it would have to be signed at the courthouse or in front of a notary. If not, people would be doing fraud all the time.

So call the police and report the fraud.

Actually, if he was proven to be the legal father in court, or through a paternity affidavit that was accepted, the birth registry should be amended, and he should be included on any copies of the birth record going forward. I think that the OP may not have the entire story.

Agreed, we do not have enough info here. First, We would need to know the general locale to determine prevailing laws. Second, I can't see a registrar amending a birth certificate just on the mother's signature.

So there has to be more to this story.