Contact the police, and make sure you tell them you are reporting fraud. Otherwise, you may get an officer trying to dismiss it as a "civil" matter. If the amount of the check is sizable, the police should take an interest.
The response I have provided is general in nature, and does not create an attorney-client relationship. My practice is based in Rhode Island, and the law and practice in other states or jurisdictions may be different.
You should call the police and report the fraud.
This is general information and not legal advise. This communication does not create a lawyer-client relationship.