How to prove that a signature is indeed mine or not mine?

I have encountered a situation where a signature on an important document is being questioned, and the parties disagree whether it is my signature. Since I have read that the Supreme Court recognized handwriting expertise as the only proper evidence regarding the authenticity of a signature, I want to ask: if I am sure that the signature on the document is not mine, but I did not initiate a handwriting examination earlier—can I still request it now, and how should I properly do this in court proceedings? Is there a risk that the court simply will not consider my arguments without such an examination?