A quitclaim deed is not going to get you off the loan. (I'm also puzzled as to what the quitclaim deed is supposed to do as that is a transfer of a title interest. Whose transferring their interest, you or your sister?)
Anyway, if you haven't notified the lender that you didn't sign the loan, you should consider whether you want to do that (and, depending on when it was signed and when you knew about it, you may run in to some problems with trying to get out of it now). Also realize that if you notify the lender, the lender may take legal action and it could be both civil and criminal (and, in the civil context it will have to involve you and in the criminal context it may involve you). You both could lose the property as well. (As I'm also unclear as to what deal, if any, you made with your sister, I'm not sure what to tell you as this is likely to effect the analysis as well.)
Bottom line: I would strongly encourage you to consult with an attorney before you do anything further w/r/t the bank, the police or even your sister.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.