A slight deviation from the properly messaged, street legal license plates, this custom tag sharing a great naval tradition. Celebrated as one of the US Navy's finest rituals is the Shellback, an initiation for first-timers crossing the Earth's equator. More formally, the "line-crossing ceremony," where Pollywogs become Shellbacks, pays tribute to King Neptune, the God of the Sea. Some element of pain, I've been informed, is involved. The owner of this license plate, seen in Murfreesboro, TN, served aboard the USS Mahlon S. Tisdale, a guided-missile frigate.