NCIS Season 1 Episode 6

Tony: Just accept the fact that you're going to get lost.
Kate: Why do you assume I'm going to?
Tony: Because everyone does. Carrier is a big and confusing place first time on board.
Kate: Duly noted.
Gibbs: Numbers are stencilled on the bulkheads. First one tells you the deck level - they're called bull's-eyes.
Kate: Deck level.
Gibbs: Second one, the frame number. Third tells you the compartment's position in relation to the ship's centre line. The last letter tells you what the space is used for.
Tony: Crossing from port to starboard or starboard to port isn't as simple as going straight across.
Gibbs: Sometimes you gotta go up one deck and down another.
Tony: Or down one deck and up another.
Gibbs: Sometimes two.
Tony: It's frustrating.
Gibbs: Not to mention confusing. But you'll get the hang of it...
Tony: ...After you get lost a few times.