How hard is it to cash a paycheck that is signed?

I signed my paycheck because yesterday I thought I was going to cash it. The place where I was going to cash it turned out to be closed though. I decided to cash it today but I just noticed that I can't find my paycheck and looked everywhere. I guessed it must have fallen out of my pocket. I called my boss and he said its cool all they have to do is cancel the last paycheck and give me a new one. What Im worried about is if someone already cashed it. Is it difficult for someone to cash a signed paycheck?|||no not difficult at all