Legalize it !!!

This poster is based on a wordplay. It's difficult to translate in English.
I don't say I agree to use drugs as marijuana but the idea to choose this date is funny.
Try some explanations :

• Joint = spliff
• Appel du 18 juin = Appeal of 18 june by Charles De Gaulle in 1940
• juin and joint have similar pronunciation
• L'appel des 18 joints = Appeal of the 18 "spliffs"

So, the association chooses this particular day to demand the legalization of marijuana.