Sorry this happened to you.
Sounds like an excellent case to me. I handle matters like this throughout CA.
I have a friend I refer similar case to (in NV) who does excellent work for consumers in trouble.
Please contact me directly and I will make the connection for you.
The terms of the warranty are key here. There is a huge difference between a "power train" warranty and a "bumper to bumper" warranty. Plus each company has terms specific to their warranty program. You generally grant a limited power of attorney for the dealership to register the car for you. Generally this limited power of attorney does not have anything to do with the warranty. If a signature was forged, the forging party committed a felony in the State of Nevada.
As suggested by Mr. Boley, we would need to know which paperwork they placed your signature on. It's only forgery if they didn't have your permission.
Also, most warranties like that are not through the dealer, but a third party, whether an insurance company or an organization formed by mechanics to let them compete nationally.