Upper quadrant and lower quadrant semaphore signals have similar indications. The highest an upper quad signal blade can raise is to the vertical position almost universally known as clear. The middle position or angle of approx 45 degrees was approach, and the lowest position resulted in a horizontal position of the blade which meant stop.

a lower quad set up, the highest a blade could go was horizontal or stop.

the middle was a 45 degree angle or approach.

the lowest was a vertical blade which meant clear.

the upper quadrant signals prevailed over the lower quadrant signals because under a lack of power the blade would fall to its most restrictive indication ....stop. If snow built up on the blade and its weight forced the blade down, the upper quad signal would show stop. All better than a lower quad which could fail in the clear position, something that was highly frowned upon.

in my limited experience lower quad signals were usually on order boards at manned operator locations. They were usually hand operated.

Krinker, I haven't been around long enough to have ran on semaphores but we had to learn them when I hired out. For what reason, I'm not sure.

In 2005, the removed all the old semaphores on the Hinckley and Brainerd Subdivisions and scrapped them. They left one at the Central Ave Junction entering the Lakes Subdivision from the former NP mainline. (Now used as a running track to Midwest Energy Coal Plant).

I should pay more attention because I think they might of cut that one down as well.

Here is a good story as well as some cool old pictures of the Central Avenue Junction

http://zenithcity.com/james-j-hill-takes-northern-pacific/