memorial slab
A monument of a very simple kind, consisting of a slab of granite, marble, or the like, usually set against or built into a wall, and bearing an inscription, or, as is frequently the case, carrying a secondary slab or thin plate of metal upon which the inscription is engraved. Such slabs, costing but little and occupying but little space, are in modern times the most common memorials other than those erected immediately over graves. (Sturgis, 1900)