What is a "highball signal"

A highball signal is another name for a clear (green) signal. The term dates back to the early days of railroading, when a white ball was hoisted high on a post to indicate a train could leave the station.

Highballing also refers to operating the locomotive at its maximum speed, which is rarely done since railroad rules and signals dictate the maximum authorized speed (MAS) along a section of track.

-John

Actually there is a "proceed" hand/lantern signal which consists of the man on the ground repeatedly raising and lowering his hand/lantern vertically (not in an arc). A quick search with railroad hand/lantern signals will show it and a bunch of others as well. The "proceed" is equivalent to "let's highball" or "let's get down the line". That said, I am sure somebody will contradict me tomorrow during daylight hours.  

And here's where the term came from:

With the ball in the high position, it meant all clear.

Jon

Here ya go (In my best Farmer Bill voice) :

That North Conway Station sure looks good.

two that I made up:

- walt

See "Proceed" on the lower right.

Rusty

The highball signal, also known as the cocktail flag, is hoisted to the yardarm of a moored or anchored yacht to indicate that the owners are observing cocktail hour, and friends are welcome to join them.

Ok this sparks a possibly related question. The term "low ball" or "low balling", in the context I've always heard the expression, "he low balled me on that estimate". Was this derived from the railroad ball signal in some way, or just similar but unrelated?

I've added to this post. I checked the net. I found one source that indicates the railroad signal (Stop) as the origin but does not explain how it evolved to the current usage.

low-ball or low·ball (lō′bôl&prime

We use the term "highball" regularly now days even though those types of signals do not exist any more. Proceed, keep going, don't slow down, a-head, lets go, don't stop, etc etc etc

Are we gonna spot that plastics car tonight? Nope, highball it!

Air test is complete, we're ready to go. Highball!

We don't really use hand signs or lantern signs to say highball. "Proceed" shown in that chart above, basically means ahead, pronounced as we say it, "A HEAD", meaning go forward. When I'm giving hand signs to an engineer (or lantern) it's ahead, back up, easy, stop, etc etc. Once we are doing switching, building the train or whatever we are doing, once I climb up on the lead unit, I may tell him "Highball" or "A HEAD"! meaning lets go!   

Since we are on this subject, how about "balls out"?

Definition,The original phrase is actually hinted to in the expression "with a full head of steam". In the earliest days of steam engines, Watt style engines and their successors used a centrifugal governor to control speed. The faster the engine was to run the higher the weighted balls on the governor would rise until at full speed they were at their highest and farthest reach from the center: high or full speed was known as running "balls out".

Thanks Jerry and Rusty, etal  that was the info I was looking for.