Is 4/20 Vandalizing of Sparty Statue an U of M Fan Tradition?

Someone -- a University of Michigan fan, seemingly -- defiled the statue of Sparty on the campus of Michigan State University, with the words "Go Blue."  The blue painted words that were added to the statue over the Easter holiday weekend seem to mark a tradition of vandalism that occurs at about the same time each year -- perhaps a holiday of a different sort.

An MLive.com article posted on April 20th of last year shows Sparty got a UM-themed makeover on that weekend as well, begging the question, is this intended to become an annual event?