The annual Worldwide Marijuana March, also called Global Marijuana March, Million Man Marijuana March and so on is held on the first Saturday of May every year. Dana Beal in New York strongly encouraged and sponsored up to three hundred plus cities around the world for several years until he was arrested and imprisoned. 2016 event will be Saturday May 7.
Broken link - They changed their domain name and their "Archives" only go back as far as Oct. 2011.
A image gallery of the Calgary 2011 event is at http://calgary420.ca/gallery/2011/worldwide-marijuana-march
There is a short piece of the missing Calgary Journal article that was published April 29, 2011 at http://calgary420.ca/forum/index.php/topic,3132.0.html