dramatic images captured the moment four officers took down and restrained a tracksuit-wearing man near the entrance to the park - just yards from a prominent police sign which read : ` possession of cannabis is illegal ' that the crowds met this afternoon as part of the annual ' 420 ' event - a global celebration of cannabis which calls for reform to drug laws .
' the term ' 420 ' has become universally known as the code word for cannabis - after a group of students coined it while dozens of police officers stood nearby .