Effective Date Of 1860 US P.o.d. Ruling

On page 7 of U.S. POSTAL MARKINGS 1851-61 Second Edition Revised and Enlarged by Thomas J. Alexander, under a heading of;
"Letters Prepaid by Stamps A townmark showing the name of the town and state, as well as month and day deposited in the post office. The stamp is cancelled, either by the townmark or by a separate obliterator. (In 1860 the P.O.D. prohibited the use of the townmark as an obliterator)."

When in 1860? Anyone have any more specific date?

The very first article that I ever wrote for a national newspaper or stamp magazine was about a First Day of Rate Cover (1883) in the March/April 1974 issue of First Days, the publication of the American First Day Cover Society. When I initially submitted the manuscript to Sol Koved, the editor, he returned it and asked for further elaboration. One of the things that I did was to mention that the PMG ordered that the date and town mark not be on the stamps themselves. This order was dated July 23, 1860. Unfortunately, I can't tell you where I found that information.

Thank you Glenn. I came across the reference twice yesterday, and both authors mentioned it rather vaguely " In 1860, the POD prohibited the use of the townmark as an abliterator".. Here, someone remembers the date!