Anymore..........
....highball has many railroad uses, and doesn't really describe any lineside signals. What is most common is a crew member of one train inspecting another as it rolls by, looking for potential mechanical problems. If he is alert and finds none, or is off throwing rocks at turtles in a pond and sees none, he hollers at the train as it roars off into the dust "highball so and so" and they'll more often than not respond back with "highball so and so"- where so and so could be the train symbol, or the name of the siding where they are meeting at, or the engine number.
Awhile back, on my railroad in a location not far away, a crew was snoozing in the wee hours of the AM as they set in a siding awaiting an opposing train- a loaded coal train. I believe they said the weather was a bit damp and cool. Good sleeping weather! Anyway, here comes the train into view down a long piece of tangent track. The snoozing crew continues their snooze and no one watches the train by. Without batting an eye(lid) the train passes them and as soon as the rear end of it roars past, the snoozers "highball" the train via radio and then come to life to get ready to leave.
Not less than a few minutes later, the train they failed to watch by goes into emergency as it is going over a defect detector and the detector doesn't do it's normal announcement.
That conductor walks his train to find the trouble and he doesn't have to go far~ a journal on a car burnt off and there were cars and coal scattered all over the place! I believe I heard it demolished the detector building along with all the other damage it caused.
In the ensuing investigation, they grilled the snoozing crew whom asserted that they most certainly watched that train by and saw nothing amiss.
Well, along comes the guys with the laptop computers. They pull the onboard camera (black box) and ship it off to headquarters for review.
Then, the heads start to roll. As the footage was viewed of the passing train, lo and behold out in the distance (remember the part about long, tangent track and wee (dark) hours earlier?) you can see a faint glow of a glowing bearing/axle, which continues to get brighter and brighter as it got closer. As that car draws near, you could actually see molten steel dripping off onto the ends of the ties as the axle was having a "meltdown".
That was the end of their defense. They got fired for lying, among other things, cause they lied about watching the train by when they didn't- Not sure when they'll be back to work.
Such is the life of a railroad man.