They are neat! Almost all remailed postal cards are the result of an invoice/bill/assessment as the original message, a payment mailed back with the card in an envelope, then the postal card is stamped and remailed as a private postcard as a receipt.
Here is one I have shown before, used during the period of April 15, 1925 - June 30, 1928 when government postal cards were 1 cent and private cards were 2 cents. Thus the two mailing cycles show both rates on one mail piece.
