MSU Rock has been a bastion of free expression for many years at Michigan State University.
Per Wikipedia:"The Rock was unearthed in 1873 near what is now the corner of Grand River Avenue (M-43) and Michigan Avenue in East Lansing, Michigan. It was donated to the (Michigan) State Agricultural College by the class of 1873. The college placed the rock in the "Sacred Space" near the modern day Beaumont Tower, where the stone became a common hangout for young couples and became known as the "Engagement Rock". By the late 20th Century, the rock had become better known for protest slogans than engagement photos. In 1985, it was moved to its current location, east of Farm Lane, on the north bank of the Red Cedar River. Today, the innumerable layers of paint obliterate the original inscription: "Class '73"."
You shouldn't need any hint other then the short description name. Might want to bring your cache monkey with you though, if you don't want to attract undue attention especially if you're old as me!