Yes if you're found guilty and are prosecuted for forging a signature on something then yes it's a Felony in all Fifty states and if Found Guilty and charged you could face jail time or even prison time over the forged signature.
The penalty for forging a signature can be from a $2,000.00 fine, 1 year in jail or even 10 years in prison depending on the severity of the case of the signature being forged.