On the Washington State Ferries I've been on (mostly on the Anacortes-San Juans route), they are marked "No. 1 End" and "No. 2 End" in various places on the vessel.
And, no, that does not describe the heads and their use...
For anyone interested, we did a video story on the recent first sailing of the year of the WSF ferry that connects the US and Canada. It's for our web site up here that is dedicated to the San Juan Islands. That's my wife on camera...