First, on most ships, there are tack numbers above most doors or passages. These numbers aren't just for show, they actually mean something.

 

The first digit lets you know what deck you're on. The main deck is Deck #1. The one below that is Deck #2, and so on. The deck above the main deck is Deck #01, above that is Deck #02, and so on.

The second digit, separated from the first by a tack (-), is the frame number, and lets you know how far back along the ship you are. This number is the frame number which is primarily used by naval architects. The frame numbers start at 0 at the forward perpendicular and increase as you move aft. If you're at frame 60, and there are only 120 in the entire ship, you know that you're approximately amidships.

The third digit, again separated by a tack, lets you know whether you're on the port or starboard side. 1, 3, 5, or additional odd numbers indicate that you are on the starboard side. A one indicates that you are not on, but next to the centerline on the stbd side. As the numbers increase, you move farther abeam. A Zero (0) indicates that you are at the centerline. A 2,4,6, or additional even numbers indicate that you are on the port side, in the same fashion as before.