What are Back of the Book Stamps?

Lot of 62 Mostly Older US Revenue & Back of Book Stamps

stamps – Chewing with the Paper Chipmunk

DS170 - Volume I, Mystic's American Heirloom Collection of United States Back-of-the-Book Stamps - Mystic Stamp Company

Embossed Envelopes, Postcards & Back-of-the-Book Stamps.

U.S. Parcel Post Stamp Q1 Unused

CD Stamps - Canadian Recording Artists

Back of the Book - Stamps for sale on Collectors Corner

A Quick Guide to Ex Libris Stamps –

USPS The Snowy Day US Postage Stamps Book of 20 (5 Booklets (100 Stamps))

Back of the Book Stamps R50595 Worldwide - Other, Stamp / HipStamp

United States Back of the Book Stamps and Postal History Stamp Auctions