Got it! Clearly I don’t understand enough about nautical navigation to even understand the jokes.
Here’s one I found online:
An ensign on sea duty for the first time overheard a recruit say he was going downstairs. “Listen, sailor," he snarled, “Downstairs is below, that side is starboard, that’s aft and that’s port. If I ever hear you say one more civilian word like “downstairs” again I’ll throw you through that little round window over there!”
Speaking of which, are those round windows only on the left side?
On the Intra-Coastal Waterway (east coast) the markers marking the predominately North-South
route are also red and green. I just remembred GReeN. Green, right, north.