OK....first. they are Aiming Posts
Next, yes they were used and are still used today. Once a gun is surveyed or "laid" into position, the aiming post is put out as a sight reference point. This is used to traverse the gun left and right. The sight or "panoramic telescope" is set to the needed azimuth or "deflection" and the gun is traversed until the aiming post is centered in the sight.
The M14 aiming post is in two parts. Each half is one meter long, yeilding a two meter tall pole when employed.
Today, the primary reference point is the M40 Infinity Colimeter (another discussion) but the aiming stakes are used to designate secondary aiming points which would allow the gun to traverse "6400 mils" or 360 degrees in a complete circle.
For more artillery modeling info see
http://www.redleg2scale.com/RBMI%20Info/Artillery%20Modeling.pdf
Hope that helps
Rounds Complete!!