When it's time to go, it's time to go. We often announce this to people by making a statement like, "I'm outta here," "I've gotta go," or "I'm gonna jam." This is not a new thing. In the eighties people may have said, "I'm Audi 5000." This week, the old timey phrase takes us back to a different era. In the days of railroad and steamship travel it was "The Next Thing Smokin'."
When it was time to go, you could proclaim, "I'm on the next thing smokin" and you would be catching a train or a ship out of town. In those days, the modes of transport were not nearly as efficient as they are today. Steam locomotives and ships were powered by coal fired boilers. The result of a coal fire is a sooty black smoke.
My search uncovered a country song by the same name that has some entertaining album art.