I have heard the bullet strips as the origin of that one too... have read both explainations on them.
Here is one I read about (I don't believe everything I read but it makes sense) Hopefully the moderators take this with a grain of salt lol
The word s-h-i-t actually started out as an acronym...
In the old days of sailing, some of the goods shipped were dried bales of manure. When kept in the cargo hold, they often got a little damp and started to ferment. This caused methane gas to form and when the sailors came into the hold with a candle or lantern the hold would explode. After losing a few ships to these explosions they finally resorted to special markings on the bales of manure... Ship High In Transit.... or for short... S-H-I-T
Yah but have you ever smelled cheese? Some of it stinks eh?