Workaround:
The workaround is to issue the client an Adobe Sign license. Once they are provisioned an Adobe Sign license, they will be able to add a signature field directly in Adobe Acrobat without receiving an error.
Solution:
The client needs to be issued an Adobe Sign license in order to utilize the signature tool in Adobe Acrobat. Issue a Katalyst ticket on behalf of the client to be provisioned with an Adobe Sign license.