From Kaplan's Encyclopedia of Tarot vol. 3:
"One of the most reliable methods of dating a tarot deck is to locate and identify the tax stamps, which may appear on one or more cards in the pack. Since the 16th century, governments of certain European countries, notably Austria, France, Germany and Italy, have imposed taxes on playing cards, including tarot. [...]
"The history of tax stamps on playing cards in preunification Italy (before 1860) is made more complicated by the changing boundaries of the various kingdoms, by the vicissitudes of the governments, and by the intricate customs and duties upheld by each kingdom to protect its own industries. After the unification it is considerably easier to identify Italian tax stamps and to use the information as a means of dating decks of cards.
"The tax stamps on Italian tarot decks generally appear on the ace of coins or on the king of batons [...]
"Laws granting concessions to gather taxes on playing cards started in the various Italian states at the end of the 16th century: 1588 in Bologna, 1606 in Lombardy, 1616 in Venice, 1619 in Tuscany and thereafter in Piedmont. By the beginning of the 18th century the practice of tax collection on playing cards was widespread in Italy. By the end of the 18th century all but a few small states had abolished the concession system of taxation, and the government gathered taxes directly through its own agents."
-- Lee