Your question does not indicate how you were damaged by this conduct. While I appreciate that you did not appreciate someone deciding to sign your name, if you like your new job, then perhaps this is a case of all's well that ends well.
If, however, some adverse employment action was taken as a result of this conduct or you were damaged, then you should consult with an employment lawyer in Marion County.
Disclaimer: Please note that this answer does not constitute legal advice and should not be relied on because each state has different laws, each situation is fact specific, and it is impossible to evaluate any legal problem without a comprehensive review of all the facts and documents at issue. This answer does not create an attorney-client relationship.