Leave it to a sailor (in particular a member of the goatlocker) to explain things.
back in the days of iron men & wooden ships, occasionally the cargo would be pressed cow manure stacked on pallets and placed in the hold. During the deployment the bilge would start to gain water and the hold would become very humid. The manure would start to decay and produce methane gas. When the Sailor would enter the space with a lantern the hold would explode. Once they realized the reason for these mysterious occurrences, they started to place banners on the sides of the pallets... 'Store High In Transit!' That Sir is the origin of the word, so feel free to express as much Shit as you want anytime you feel appropriate!"
I've heard the "Stack High In Transit" thing before. But not one specifically mentioning cow shit. Just various shit that they didn't want getting wet.
My Scottish ancestors would say that story is shiite.
But still funny. O0