Suck it Fronk
From Halopedia, the Halo wiki
The words Suck It Fronk is an easter egg in Halo 3's new DLC map Longshore. It is located inside the freezer and and easier to see with the turret glitch. The words are on the right hand side but must be seen at an angle in order to fully read, as it is hard to see when looking straight at it.
It is a bitmap and takes no effect when a grenade is thrown in its direction or shot at.