Power of attorney is a legal instrument whereby you, as the POA, are legally enabled to act as, and in the interest of, the person for whom you have been granted POA. That said, when signing documents, you have to follow a slightly different procedure than simply signing your name or the name of the person for whom you have POA.
After completely filling in the information on the check (to whom it is payable, the amount of the check and the applicable date), sign the name of the person for whom you have POA on the signature line.
Beneath where you have signed that name, print your own name, followed by "Attorney In Fact For." Then print the name of the person for whom you hold POA.
When endorsing a check for deposit, sign exactly as you would when issuing a check; however, sign on the reverse of the check, as you normally would.