I think it was back in the late 1980's. Apparently you could buy stamps for certain quantities, and also a dealer's license. I believe they were available at the post office. It was so that you would not get busted for tax evasion. I always wanted to buy some just for kicks and frame them, and it sounds like a great idea when you're high, but I don't really want to put my neck out like that.
If I remember correctly, when marijuana was first made illegal; you could only possess it if you had a marijuana tax stamp. But the government didn't give out any stamps. Or something like that.
From: http://en.wikipedia.org/wiki/Marijuana_Tax_Act In the United States, the 1937 Marijuana Tax Act (strictly the 1937 Marihuana Tax Act) was one of the cornerstone bills that led to the criminalization of Cannabis. It was introduced to U.S. Congress by Harry Anslinger, then Commissioner of the Federal Bureau of Narcotics. The act did not itself criminalize the possession or usage of marijuana, but levied a tax equalling roughly one dollar on anyone who dealt commercially in marijuana. However, its penalty provisions were unusually severe--violations of proper procedure could result in a fine of up to $2000 and five years' imprisonment. The related paperwork was unduly complicated and byzantine. The net effect was to effectively make it too risky for anyone to deal in the substance. Beginning with Arizona in 1983, a number of states have revived taxation of marijuana and other illegal drugs as part of a new "War on Drugs." 24 states have used revenue stamps to evidence payment of the tax. Tax rates for harvested marijuana range from $10 per ounce (Arizona) to $100 per gram (Nevada). A few states tax unharvested marijuana plants separately, at rates ranging from $134 per plant (Arizona) to $1000 per plant (Wisconsin and Kentucky). Here are scans of the latest drug stamps: http://www.milwaukeephilatelic.org/HenakHome/DrugTax.htm
From what I know you needed a stamp to have marijuana and to get a stamp you needed to have the marijuana present. But if you showed up to get a stamp with the marijuana you were posessing marijuana without the stamp therefore you were fucked.