Post Office Type PO-A6.2B with Postage Due slogan B.
Three meters were used in a trial that lasted a little more than three years, from September 1948 to the end of January 1952:
A. 156057 NEW YORK / N.Y. (used at GPO New York, September to October 1948)[RRR for favor tape, unknown on non-philatelic cover]
B. 169333 SAN FRANCISCO / CALIF. (used at Rincon Annex, San Francisco CA from December 7, 1949 to January 30, 1952)[R for favor tape, RRRR on non-philatelic cover]
C. 170592 SAN FRANCISCO / CALIF. (used at Main P.O., San Francisco CA from December 8, 1949 to January 31, 1952)[R for favor tape, RRRR on non-philatelic cover]