Has anyone heard of this? 20 states require people to buy stamps to put on their weed. If someone is caught without a stamp, they can be penalized with tax evasion. I don't know to what degree these laws are enforced, but its absolutely ridiculous. Check the links:
http://www.norml.org/index.cfm?Group_ID=6670
http://marijuanastamps.com/state-stamps.htm