The signal surge protective device is a lightning protection device which is widely used in the terminal equipment of signal systems. In order to improve the safety and realize the fault indication function of its components, taking the complexity of the circuit and the limitation of the internal structure space into account, a new signal SPD is designed and studied, using a polymer Positive Temperature Coefficient resistance (PTC) to protect other components, and an integrated fault indicator is added. The simulation tests of overheating protection on TVS (Transient Voltage Suppression) and series resistance, as well as three tests on the impact current, transmission characteristics and overload failure modes in the SPD test standards, are conducted, and the results show that: the new product has the function of thermal protection and all the parameters meet the requirements of the SPD test standards. At the same time, the product has a passive fault indicator, which is suitable for a system that can be interrupted in a short time.