Complex sentence: Wigwag is the nickname given to a type of early, North American, 20th century, railroad grade crossing signal, so named due to the pendulum-like motion it used to signal the approach of a train.
Split into simpler sentences: Wigwag is the nickname given to a type of railroad grade crossing signal developed in the early 20th Century. So named due to the pendulum-like motion it used to signal the approach of a train.