Abstract: An indicator assembly includes a conduit segment located in place along a gas supply line served by a pressurized tank. A pressure actuated switch of the assembly closes upon sensing gas pressure in the conduit segment to close a circuit including a battery and an indicator to signal a user that the supply line is pressurized which can occur when proper shut down procedure is not accomplished or a faulty control valve. A bleed valve on the conduit segment permits venting of a pressurized gas line. A check valve of the assembly prevents erroneous activation of the indicator by residual gas trapped in the supply line after shut down.