I followed
Parcelpostguy's suggestions for searching, and once I found the original
Recorded Delivery cover, browsed the sellers past sales.
I discovered one additional Brad Arch cover, with a USPS service I had not seen used previously. The cover is obviously philatelic.
Return Receipt for Merchandise is described in Beecher and Wawrukiewicz in Chapter 51, the final chapter in the book, with no example of usage. It began in 1973 as a experiment, and became a formal service May 21, 1980. It was officially discontinued on July 1, 2020.
Like Tony, I had never seen an example of this service used, philatelic or otherwise.
I have a series of the unused Form 3804 provided for this service, which I will show next.
PS Form 3804, March 1988. The reverse is blank.
PS Form 3804, Mar 1988. Same revision date but
Mar. 1988 rather than
March. 1988 design. It is unusual to have two revision dates for the same form with different designs. The reverse is blank.
PS Form 3804, July 1999. The bar code added. The reverse has instructional text shown in a later example below.
PS Form 3804, Feb 2000. The bar code added. The reverse has instructional text.
PS Form 3804, July 2002. The bar code added. The reverse has instructional text.

And the reverse...
Edit: The text is the same on each reverse, printing is slightly different.
And after all this effort

, I discovered that John Becker has added ten different varieties of this form into the Stamp Smarter Forms database found here:
https://stampsmarter.org/features/N...ms_Home.htmlMike