It's probably a local occupation stamp, or something like that, and won't be in Scott. It may be in Michel, but I don't know offhand if it can be found under Germany or Italy.
There is a web site that shows genuine Overprints of these 1943 Occupation of Zara stamps: https://stampforgeries.com/forged-stamps-of-zara/ Hope this helps. Scott
Michel lists these under "Zara" in its German Occupations 1938/45 listings in its German Specialised catalogue. SG lists these under "German Occupation of Dalmatia" at the end of its Yugoslavia listings in its Part 3 Balkans catalogue.
Unable to find this stamp listed in Scott catalogue? Need catalogue number reference. 
