Patent ID: 7009513

Claim:
In combination: a sub-grade structure having a peripheral sidewall including an upper rim forming an open top above a cavity inside said wall; a cover adapted to fit in said open top to close said cavity; and a warning device so disposed and arranged as to give visual notice of the open condition of said open top when the cover is raised or removed, said device comprising a hinge plate mounted to said upper rim inside said cavity; a hinge pin rotatably fitted in said hinge base; a spine on said hinge pin rotatable between an upper deployed position and a lower position below said rim; a placard mounted to said spine; and bias means biasing said spine toward its deployed position; whereby with the cover laid atop said rim, the spine and placard will be held in the cavity, spring-loaded against the cover, and when the cover is raised or removed, the spine and placard will rise above the rim.