Long ago (when men were bold....woops getting carried away there) dried manure used to be shipped around Britain's shoreline.
If stored in the lower decks then it ran the risk of getting damp thus creating methane and thus ships from time to time exploded and sank.
Having worked out what caused the explosions the ('elf 'n' safety) powers that be decreed that all crates of manure were to be stored on a higher deck with an appropriate warning stencilled on the side. Thus:
Store
High
In
Transit
or poop for short.
So there you go, it's an acronym.
And not a lot of people know that.
(Just thought I would share this with you for when it's next quiet in the snug and you want to think of something to share.)