You may want to add signature using Signature service which has lot of options to customize signature appearance.
Please advise in more detail on how to add the signature field in offline Adobe PDF form using Signature Service.
This offline Adobe PDF is providing for our customers to sign with their digital certificates issued by CA other than Adobe.
Signature fields can be added to PDFs of your interest using LiveCycle ES and then can be distributed to customers for off-line signing
I'm not sure if yours is an enterprise usecase or not.
The APIs that I suggested are available in LiveCycle (server product) Enterprise suite.