In most US waters the commercial traffic uses just what you have described and they refer directly to the sound signals proscribed in the COLREGs. They are still required to sound the signal on the whistle, although not all do.
My current copy of the COLREGs is dated, but I think a careful reading of Rule 34 will show that it is only for vessel's underway. As you stated, 'Romeo' would be applicable in fog. 'Uniform', you are standing in to danger, or possibly 'Lima', you should stop your vessel instantly, or 'X-Ray', stop carrying out your intentions and watch for my signals might all have been applicable in my 'allision'.
When this incident occurred, I held my first renewal of my unlimited Master's license, which meant I'd gone through five licensing exams, and I was fully under the impression that the danger signal was appropriate. Please PM me if your newer copy reads differently, specifically in (a) of 34. Maritime law is chock full of cases dealing with just these issues-hard to believe in what, initially appears to be a very straight-forward book! Unfortunately, I had to waste a day in admiralty court to be educated on this finer point. If I had to do it over, I would probably sound Uniform, and, failing to see any response sound the danger signal. YMMV
A little understood point, except by professionals, in the differences between International and Inland rules is that sound signals made in International waters are signals of action, while the same signal made in Inland waters is a signal of intent. A subtle difference, not without distinction.
The reason I mentioned ho 102 is that it contains all of the single letter signal meanings, as well as multiple letter/number signalling. There are a good number of signals, usually two letters followed by a numeral, to indicate a variety of situations, and they are part of 'Interco' which allows one to communicate via flag, flashing light, or sound signals. These are signals outside of the COLREGs.
Good luck on your renewal. I hope the "pony" hits!
Last edited by sailaway21; 03-22-2007 at 12:21 AM.