There was an article on Fergusson in TCA Quarterly a while back.
Just to complicate things, Fergusson also supplied these signals to others to sell, particularly Hafner. The ones they sold through Hafner however were mounted on square Hafner bases, not the G-shaped bend in the rod. Many of these same signs (the clock, semaphores, "whistle" sign) can be found mounted on the square Hafner base.
These accessories often show up being soild as Flyer, but that it not the case; Flyer had their own complete line. If they have the solid rod mounted on a square base, they are made by Fergussoin for Hafner; if the G-shaped bent rod base, they were most likely sold by Fergusson. Some Ives signs, particularly their telegraph poles, look very similar, but Ives used a hollow, rolled tinplate post instead of the solid rod.