Abstract: The present invention is a signaling device for indicating passage of a pig through a pipeline. The device attaches to the pipeline by means of a nipple welded to the pipeline. As a pig travels past the device, an actuator of the device which hangs down into the pipeline is pushed upward by the pig. The actuator causes a spring biased plunger located within the device to move upward, causing a polar magnet attached to the plunger's upper end to approach a rotatable magnetic indicator ball. The ball is colored black on an upper half which is initially visible through a clear dust cover provided on the device and is colored yellow on a lower half. The upper half of the ball is of opposite polarity and the lower half is of like polarity to the polar magnet.