To answer this question, we need to go to the source document, the Revised Code of Washington, Title 11, Chapter 11.125, Section 11.125.050. Aka RCW 11.125.050 states:
“the signature must be either acknowledged before a notary public or other individual authorized by law to take acknowledgments, or attested by two or more competent witnesses”
The POA must be signed by the principal and either notarized by a notary or (not “and”) two witness. It’s an either/or answer.
Often the form will have an area for the notary to notarize. In addition there will be lines for witness signatures. The UPS Store will take one look at the lines for witness signatures and require two witnesses. According to RCW 11.125.050, a POA can be either notarized or witnessed. Ideally, the POA will have both.
NOTARIAL SERVICES, ETC 