If there is no court order (your post says she has had the child voluntarily by you), you mother appears to have no legal rights to "sign over". This does not mean, however, that proceedings cannot be started by the state or a third party for custody if you have abandoned the child or failed parent the child. I recommend you consult with a family law attorney to go over your facts in more detail.
You need to talk to an experienced family law attorney who can learn all the facts and review any current legal arrangements as well.
If your mother currently has a legal 3rd party custody order, then that order should state what rights you have as well (visitation?). As with any parent, she can delegate her rights to 3rd parties, and allow you to see the child for periods of time if she desires. To give you legal custody, even temporarily, there would have to be a court order.
Sign up to receive a 5-part series of useful information and advice about child custody law.
Our Rating is calculated using information the lawyer has included on their profile in addition to the information we collect from state bar associations and other organizations that license legal professionals. Attorneys who claim their profiles and provide Avvo with more information tend to have a higher rating than those who do not.What determines Avvo Rating?Experience & background
Years licensed, work experience, educationLegal community recognition
Peer endorsements, associations, awardsLegal thought leadership
Publications, speaking engagementsDiscipline