I signed my wifes name when I cashed a check made out to us jointly? Did I commit the crime of forgery?

Your situation is not uncommon. Each state has its own laws against forgery and penalties for check forgery in particular.  However, it is universally true that the crime of forgery has three elements that must be proven (1) a document that is apparently genuine, e.g., a check, (2) a name signed that is fictitious, e.g., one person signing the name of another, and (3) a fraudulent intent on the part of the person signing.  The third element is clearly absent in your case and is why the authorities usually don’t prosecute these cases as criminal conduct. Banks know this very well and the teller should not be harassing you with these kinds of threats. Nevertheless, threatened criminal prosecution is always a serious matter and you should consult an experienced criminal defense attorney for advice on how best to handle this situation.