An overpressure indicating disk apparatus for indicating an over pressure condition in a pressurized system includes a body having first and second end portions and a bore, the first end portion configured for attachment to the pressurized system and in pressure communication therewith so that the pressure in the bore is the same pressure as the pressure of the pressurized system. A reverse buckling disk having an annular peripheral portion and a concave convex dome portion is provided. The annular peripheral portion surrounds the dome. The disk annular peripheral portion is mounted to the body, closing the bore at the first end portion. An indicating component or ring is affixed to the combination of a body and reverse buckling disk. The indicating ring has an annular peripheral portion that aligns generally with the annular peripheral portion of the reverse buckling rupture disk. A movable central tab portion is mounted inside the indicating component or ring. A hinge connects the central tab portion to the indicating ring. The concave side of the reverse buckling disk faces the central tab. The convex side of the reverse buckling disk faces the pressure inside the bore. When the pressure in the bore exceeds a preselected maximum pressure value, the disk reverses to engage and displace the central tab thereby indicating visually that an overpressure condition exists within the bore.