Another person may NOT bind you to a contract--and that's what a lease is: a contract--without your consent. You are not liable to the landlord or obligated to the lease if you did not sign it, though if the landlord believes you did and take legal action against you, you will need to testify and ideally provide other evidence (e.g. other people's testimony; evidence of a lease where you did live instead) to show that you did not sign the lease.You can sue your roommate for any costs, losses, or damages you suffer due to her falsely representing that you signed the lease; depending on the exact circumstances, this could be identify theft or fraud.You also should file a police report and probably press charges against her: what your roomate did is crime, and filing a police report will help establish that you did not sign the lease.