Signals

Scales from 2mm to 7mm to the foot.

Servo operation, with or without simulated bounce is also possible as well as installing working lights where feasible.

There are also options for jig-built laddering etc and additional detail.

A few notes on construction:

Tubular posts are made from brass tube
Square Posts are usually made from etched brass or Nickel Silver to my own design. In 4mm scale concrete posts are from etched nickel silver (Nobody has asked for them in 7mm scale yet). 7mm, 4mm and 2mm scale - etched brass
Lattice posts from etched brass/nickel silver
Operating wires from Nickel Silver wire, thickness depends on scale.
An increasing number of brackets not available elsewhere, mainly in 2mm and 4mm scales (Great Northern and LSWR) but some in 7mm scale (GCR and GWR)
How many arms? It depends on the design. Normally anything over 6 using SG90 servos will be problematic. Fortunately there is a solution with the latest ultra small servos. They are more expensive to buy and require additional electronics to operate with one of the normal control boards.

Other Signal Parts:

4mm scale Alan Gibson Workshop, Wizard Models, Modelu, Scalelink
7mm scale Wizard Models Modelu Scale Signal Supply
2 and 3mm scales Wizard Models, Modelu
Working Lamps - I use warm white SMD LEDs, that fit in lamp castings for 7mm and 4mm scale Either 0503 or 0402. Even Modelu 2mm scale GWR lamps can just about fit the smallest LED (0402). LEDS are fitted with protective resistors, usually 1K They can be wired into the servo leads if required.
Servo Boards of your choice. Each have their strengths and weaknesses.
Gantries can also be supplied but costs vary depending on scale and specification.
Fibre optic cable can be used for lighting but prefer not to if I can avoid it. The problems with it are that, it is easily damaged by handling, contact with paint, solvents or adhesives. The amount of light transmitted is less but sometimes it is the only viable option