What does the yellow G sign mean on the railroad signal ?

Question

I have noticed on a few railroads in US that there is a sign on the signals that is yellow, and shows a G. What does it mean to the engineer?

Answer 1

Andy is right, we always called 'em a Go signal bacause they dismissed the need for stopping and then proceeding at restriced speed.

Because trains are extremely difficult to start on heavy grades, in  some places we are allowed to simply pass at restricted speed but dont have to stop first.

Answer 2

It's called a grade signal.It means you can pass it when it's red without stopping at restricted speed.You'll notice that all the signals you see them on also have a number plate which means they are an abs signal.A rule change on the UP railroad allows us to pass an abs signal without stopping now so they are basically the same as a grade signal.They did that to save fuel as it burns a lot of fuel having to stop and start a train.