Abstract: The apparatus includes a sign and clips which support it. The sign is installed against the wall of the opening into a hazardous, confined space. The sign is a strip of flexible signboard with indicia applied to both broad surfaces. There are several presentations of the message of the sign on each side with adjacent presentations inverted. The clips are attached to the wall of the opening so that the sign is supported at its lower edge to prevent it from falling into the space. The ends of the sign overlap so that a sign of one length is usable in a range of sizes of manholes.

Abstract: An identification module and identification determination circuitry are provided for the purpose of identifying an apparatus and electrically determining the identification number of that identified apparatus. The identification module comprises a plurality of resistive identification circuits which, in turn, each comprise a plurality of resistive elements selected to have resistive magnitudes that relate to each other by powers, or orders, of two. The identification determination circuit of the present invention places each of the resistive identification circuits in series with a resistor of known magnitude between two connection points to provide a voltage potential and a resulting current flowing through the resistive identification circuit. The invention also provides a means by which the input voltage can be determined and used to adjust the determined magnitude of the resistive identification circuit.