It depends. You generally have to be in a given trade to take courses specific to that trade. There are, however, courses that are not trade-specific. As a Sig Op, you can reasonably expect to take driver courses, to include some AFVs such as Bisons. Do not, however, expect to go on Leopard Gunnery or Recce Patrolman. Bear in mind that your initial set of training (Developmental Period 1 or DP1) will include CF and Army skills in addition to your core trade skills, and future leadership courses (PLQ etc) will not be trade-specific.
In addition, as a Signal Operator you may also find yourself in a non-Sigs unit after a while (all units have signallers in some capacity). As a result, you should have some variety in your career if thats what you're worried about.
Cheers