Sorry you are going through this, many times they have notaries in the prison that can attest to a signature. take care.
Legal disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of Massachusetts. Responses are based solely on Massachusetts law unless stated otherwise.
I would recommend inquiring with the jail, they often have procedures in place for individuals who are incarcerated and wish to marry. They will likely be able to tell you how to proceed.
Check with the business office at the prison to see if they have a notary. You can also check with the local legal aid office to see if they can help.
The answer provided here is general in nature and does not take into account other factors that may need to be reviewed for a more precise answer. You should consult with an immigration attorney before taking any action. The answer here is not intended to create an attorney-client relationship.