First and foremost NEVER let a signer use the term POA. This is not an established abbreviation for power of attorney, POA could be used to indicate Paid On Account.

Refer to your state statutes or notary division.
Some states will require the notary to view the original Power of Attorney, others states say the notary is not allowed to refuse notarization if the signer does not produce the power of attorney. So this is a case of KNOW YOUR NOTARY LAW.

In situations where this is in conjunction with a loan package, you do need to call the client (lender, title company etc. to ensure that they are willing to accept the Power of Attorney (some do not).

Most commonly accepted way for the individual to sign using power of attorney is one of two ways:

Susan B. Smith by Joe D. Smith as her attorney in fact
- or -
Joe D. Smith for Susan B. Smith as her attorney in fact;

Documents would be initialed as:

SBS by JDS
- or -
JDS for SBS

If in doubt and the document is not drawn with the signature line showing how the document preparer requires the document to be signed, call the client and ask. It is better to ask than guess at it.