The above Interpostal Seals Catalogue was published by George Chapier in French, April 1950, 23 pages . Chapier referred to the Interpostal Seals as “Vignette de Franchise”, which means Franking Stickers.

Click to downlode the catalog in pdf formate

The publication above by O. May, is the earliest known attempt to fully catalogue the Interpostal Seals. It was published in August 1915 by the London-based Fiscal Philately Society, it contains 40 pages with various illustrations.