Cartaz (plural cartazes, in Portuguese) was a naval trade license or pass issued by the Portuguese in the Indian ocean during the sixteenth century (circa 1502-1750), under the rule of the Portuguese empire. The British navicert system of 1939-45 shared similarities with it. Its name derives from the Portuguese term cartas meaning letters.
The licensing of vessels by the Portuguese was initiated by Prince Henry the Navigator in 1443, with the consent of the king and the Pope, when he decreed a monopoly on navigation in the west African coast, starting a Portuguese Mare clausum policy in the Atlantic Ocean. Ships began to be licensed by Portugal, which authorized and supported navigation, in exchange for part of the profits (usually 20%, "the fifth"), encouraging investment in exploration travels by Portuguese and foreigners.
The "cartazes" licensing system was created in 1502 to control and enforce the Portuguese trade monopoly over a wide area in the Indian Ocean, taking advantage of local commerce: the cartaz was issued by the Portuguese at a low cost, granting merchant ships protection against pirates and rival states, which then abounded in these seas. However its main purpose was to ensure that merchants paid the tax in Portuguese trading posts, directing them to the feitorias in Goa, Malacca and Ormuz, guaranteeing its monopoly on the spice trade and other products.
Officially, no vessel was permitted to sail in the Indian coast without this document, risking losing their cargo, being attacked and even sunk by the Portuguese - mainly Muslim, Hindu and Malay merchant ships. Every year, during the monsoon, Portuguese fleets patrolled the coasts requiring this document. Later, as Portuguese lost influence, the issue of cartazes become in itself an important source of income for the crown.
The cartaz system eventually introduced a new word, kadalaas (കടലാസ്) to the Malayalam language of Kerala which is till date used to denote any kind of paper.  The same with the Thai word krà.dàːt (กระดาษ) and other Asian languages.
- Boxer, Charles Ralph (1969). The Portuguese Seaborne Empire 1415–1825. p. 48. Hutchinson. ISBN 0-09-131071-7. https://books.google.com/books?id=BChmAAAAMAAJ&pgis=1.
- In 1443 Prince Pedro, Henry's brother, granted him the monopoly of navigation, war and trade in the lands south of Cape Bojador. Later this law would be enforced by the Bulls Dum Diversas (1452) and Romanus Pontifex (1455)
- M. D. D. Newitt, "A history of Portuguese overseas expansion, 1400-1668", Routledge, 2005, ISBN 0-415-23980-X, p.24-25, 30.
- Bailey Wallys Diffie, Boyd C. Shafer, George Davison Winius, "Foundations of the Portuguese empire, 1415-1580", p.274, pp.320-323, U of Minnesota Press, 1977, ISBN 0-8166-0782-6
- "The Infamous Portuguese Cartaz", http://historicalleys.blogspot.sg/2012/05/infamous-portuguese-cartaz.html