In TRS2006, I like to use the Whistle Sign Rule <kuid:70049:20001>. You don't even have to put signs on the route (you can if you want). It lists all trackmarks and will put an invisible whistle sign at the ones you select. The horn sign included in TRS2006, that you place on the tracks, doesn't work well for me. Sure, the train blows the whistle, but it is a very abreviated and anemic toot, not a nice long wail.
Zorronov