If incandescent, as posted above. it doesn't matter. Neither positive or negative will be in contact with the housing in a marine nav light, most of which have plastic housings anyway. An incandescent bulb is a glow from the resistance of a filament and it matters not which lead is at which end of it. On an LED light, positive has to be connected properly.
Interestingly, most marine interior dome lights switch negative if you go by color coding - black through the switch and white or red direct to the bulb. I usually reverse these when I install them.
Living aboard in Victoria Harbour