For nearly 50 years the Missouri Tigers football team wore black helmets with an M on them. From the incredible successes of the 1960s teams, through the doldrums of the 80s and 90s, to the resurgence under Pinkel in 2007, each Tiger squad wore a black helmet with an M - under variations of white and gold - on the side.
Missouri ditched the Block M in 2012 when they moved to the SEC. Nike provided a uniform overhaul, including the helmets, because the block M was not brand-specific to Mizzou, as evidenced by Michigan, Marshall, and basically any other school that starts with an M.