Forged promissory note, how to prove

Hi,

How to prove the signature on the document or promissory Note is forged.

what is the success rate of Forensic Science Lab (FSL) in proving Forged signatures and documents.

Any 100% guaranteed evidence to prove that the signature and document is forged in the court of law,

what is the Court perception towards FSL Report about the forged documents and Signatures.

Thanks!