Color light signals use a variety of different mounting systems.  They generally allow for positioning of the light on two axes like the mount in the photo pictured below.

Drawings of the mount shown above.  This is a relatively modern mount found in common use today.

The mount shown in the drawing to the left is a rather radical departure from prior designs.  It is adjusted by loosening the nut on the bottom and rotating the cupped top over a ball shaped support.  Once initially adjusted and locked down with the nut on the bottom, two slotted set screws in the top of the cup are tightened against the ball shaped support for further rigidity.  It allows nominal adjustment on the third axis as well.  While radical in design, this mount was not well received and is no longer used in new installations.

Below.  Ground mounting bracket I fabricated to accept the cupped top - made from glued up medium density fiber board and a pipe coupling.  Unlike the original design, a bolt attached on one end to a pivot inside the pipe fitting extends through the top cup.  The top cup is then attached to the base with a washer and a nut.

These are examples of older mounting brackets.  They only allowed adjustment on a single axis without loosening the signal from the mast.