They are local German occupation stamps of Zara. The Province of Zara (Italian: Provincia di Zara) was a province of the Kingdom of Italy, officially from 1918 to 1947. Scott does not normally list local issues.
Michel lists them in the German Specialized under Zara, MI 2 through 6. They are just a few stamps from the full set of 19. Michel warns about fake overprints. I don't have current values, but these used to run around $5 each ($10 each for the 15 cent stamp) for never hinged.
I have found the Michel Catalogue to be far more helpful with the multitude of overprints, occupation stamps and sub types that exist from Europe. You can find many used copies online. Mine ( in German), makes it a little slower for me as I have to use translator Aps, but it is worth having that reference source.
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Michel lists them in the German Specialized under Zara, MI 2 through 6. They are just a few stamps from the full set of 19. Michel warns about fake overprints. I don't have current values, but these used to run around $5 each ($10 each for the 15 cent stamp) for never hinged.