A bracket signal, a collection of signal posts placed on a common platform ('chandelier') beside the tracks, always refers to a single running track. (When parallel tracks can be run in the same direction, which was uncommon in the days of mechanical signalling but is standard practice in light signalling days, each track has its own signal.) A bracket signal is a branching signal, also called junction signal, announcing the divergence of tracks ahead. The whole bracket signal represents just a single aspect for a single track. This is different from UK practice, for instance, where signals on brackets are used to collect exit signals for several station platforms. In the days of mechanical signalling in Belgium, multiple signals for multiple tracks on a single support were only found on signal gantries over the tracks, and only a few such gantries have existed.
The system of three-position signalling was introduced on the Belgian Railways in 1919. With three aspects for a one-arm signal, the signals are very suitable for an automated block system on a heavily trafficked line. Additional speed information is provided by a combined (stop + distant) signal on a single post, which may show four aspects. These are mainly relevant to junctions, but also when the distance between two successive signals is (too) short for safe braking. The three-position system really is the forerunner of current-day light signalling.
Information about the proper application of three-position signals can be found in Signal Rule books of the Belgian Railways. Many documents (most of them in French, some in Dutch) have been collected on this invaluable website:
If you need a signal that is not included, you could build it yourself from the library components. Or just contact the author via the Trainz forum (the Dutch thread on Belgische mechanische seinen, or via Private Messages).