My girlfriend and I separated 2 yrs ago and we have a 5 yr old son. I pay regular child support through FRO however she will not allow me to see him or let me have anything to do with him. I was thinking that I may as well sign off all rights since I can't see him. What responsibilities do I have after signing off. Do I have to continue paying support and keep him on my benefits at work.

You have the option to take her back to court and have the judge assign court ordered visitation.

Child support payment is a separate issue.

Well, since you can't "sign them off", your rights won't change.

As noted you can not just sign over rights, if she gets remarried and wants the new husband to adopt, you can sign over rights to allow him to adopt,

If you have a problem with visits, you take the other parent back to court.