I've seen it plenty of times, especially in NY/NJ. I don't think I've seen it installed new since the late 1960's though. I never installed it myself, but the first time I ever saw it was in our house that was fairly new at the time (built in 1965). It was also used for the post light in the front yard. It was the predecessor to today's all-plastic UF cable.
It was just two type TW wires and a ground, spiral-wrapped with a fabric. The outer jacket is just an oval tube made of lead.
