Seems to have turned up in 1948 Ian
"Marine navigation lights
In 1838 the United States passed an act requiring steamboats running between sunset and sunrise to carry one or more signal lights; colour, visibility and location were not specified. In 1846 the United Kingdom passed legislation enabling the Lord High Admiral to publish regulations requiring all sea-going steam vessels to carry lights.[1] The admiralty exercised these powers in 1848 and required steam vessels to display red and green sidelights as well as a white masthead light whilst under way and a single white light when at anchor.[2] In 1849 the U.S. Congress extended the light requirements to sailing vessels. In 1889 the United States convened the first International Maritime Conference to consider regulations for preventing collisions. The resulting Washington Conference Rules were adopted by the U.S. in 1890 and became effective internationally in 1897. Within these rules was the requirement for steamships to carry a second mast head light.
The international 1948 Safety of Life at Sea Conference recommended a mandatory second masthead light solely for power driven vessels over 150 feet in length and a fixed sternlight for almost all vessels. The regulations have changed little since then.[3]
Basic lighting
Basic lighting configuration. 2=a vessel facing directly towards observer; 4=vessel facing away from the observer.
To avoid collisions, vessels mount navigation lights that permit other vessels to determine the type and relative angle of a vessel, and thus decide if there is a danger of collision. In general sailing vessels are required to carry a green light that shines from dead ahead to 2 points (โ22 1โ2ยฐ) abaft[note 1] the beam on the starboard side (the right side from the perspective of someone on board facing forward), a red light from dead ahead to two points abaft the beam on the port side (left side) and a white light that shines from astern to two points abaft the beam on both sides. Power driven vessels, in addition to these lights, must carry either one or two (depending on length) white masthead lights that shine from ahead to two points abaft the beam on both sides. If two masthead lights are carried then the aft one must be higher than the forward one.[4]
Hovercraft
at all times and some boats operating in crowded areas may also carry a yellow flashing beacon for added visibility during day or night.
Lights of special significance
In addition to red, white and green running lights, a combination of red, white and green Mast Lights placed on a mast higher than all the running lights, and viewable from all directions, may be used to indicate the type of craft or the service it is performing. See "Quick Guide" in external links.
Ships at anchor display one or two white anchor lights (depending on the vessel's length) that can be seen from all directions. If two lights are shown then the forward light is higher than the aft one.
Boats classed as "small" are not compelled to carry navigation lights and may make use of a handheld torch."
Here the Lighting Rules with layout pics.
http://www.bosunsmate.org/seamanship/lights.php
Seems the yellow towing light is actually a second light above the stern light. I've also seen them low on the mast facing aft!
So for the Fire boats I guess that's a normal white stern light.
Cheers, Doug.