U.S. citizens and foreign nationals (anyone other than a citizen of the U.S.) can have their closing documents acknowledged by a commissioned notary at a U.S. Embassy or Consulate. Consular officials can provide a service similar to the services of a notary public in the United States. They will notarize documents for U.S. citizens and foreign nationals if the services are in connection with the document(s) for use within the jurisdiction of the United States.
The key is for the principal to make an appointment, not just show up and expect someone to be available to acknowledge their signature. A listing of U.S. Embassies and Consular offices with all their contact information is available on the internet at www.usembassy.gov.
When making the appointment, the principal needs to also find out the cost for the services. There is typically a $40 fee for the first notarial service requested and a $20 fee for each additional seal provided at the same time, in connection with the same transaction, due at the time services are rendered.