A signal indicator is a device or system that provides information about the presence, strength, direction, and quality of a signal. This can refer to various types of signals such as radio waves, sound waves, light waves, or other electromagnetic waves. The term may also be used in reference to visual indicators on electronic devices like cell phones, which show when there is a strong enough signal for the device to function properly. In short, a signal indicator provides information about whether and how well a communication system can transmit data or perform its intended function.