ASD, re "most of us being inland". I'm surprised at that, but I'll take your word for it.
I'm not trying to be argumentative, we get enough of that on TF. I do want to clarify my point about using horns that are in compliance and expand it a bit to horns that exhibit the expected character.
re the train horn being in compliance. If the frequency is right, then you are correct the horn is in compliance. My statement in post #27 "I don't want a deep draft ship or big tow trying to find another big one when I need them to pay attention to me." for clarification might better be stated "I don't want another vessel or ship confused by the character of my sound signal, I want them to know it's me"
Let me give you an example that could be relevant to you. You're home ported on the Columbia River where there are a lot of areas with train tracks near the river as well as some crossing the river. You round a bend to find yourself in an uncomfortable meeting situation with a big tow, been there many times myself on your river. You hail the tow on vhf 16, then vhf 13. No response which unfortunately happens. So, quite reasonably you sound your horn, this time your train horn. Do you want the tug capt to dismiss your horn because he thinks it's a train?