Estafa by taking advantage of signature

Estafa by taking advantage of signature is committed by any person who defrauds another with unfaithfulness or abuse of confidence by taking undue advantage of the signature of the offended party in blank, and by writing any document above such signature in blank, to the prejudice of the offended party or any third person. (Art. 315, par. 1(c), RPC)

Elements:

1.  The paper with the signature of the offended party is in blank;
2. Offended party delivered it to the offender;
3. Above the signature of the offended party, a document is written by the offender without authority to do so;
4. The document so written creates a liability of, or causes damage to, the offended party or any third person. (Revised Penal Code, Book II, Luis B. Reyes)