Those terms would not be considered appropriate, the train could be said to be “in rear of” the signal, or the signal “in advance of” the train.
Of course when communicating with the signalman he would say he was “at” the signal, giving both the signal number and the train reporting number. It is important that it is clear who is calling as a misunderstanding could conceivably result in the driver being given instructions intended for the driver of some other train.
Over about five decades fivog, on/in differing railways doubtless still having some character of their respective pre-nationalisation practices (not necessarily official), I have heard a few times a train referred to as ‘behind’ a Home signal, on the one hand/area when standing on its approach side, and on the other when a train has been brought completely past the Home signal – the latter for which I’ve also heard referred to as having brought the train ‘inside’ the signal. Never heard of a train described as ‘in front of’ a signal.
Partly as others have mentioned, the official terms are nowadays that a train (or certain other items) is either ‘on the approach to’, or ‘beyond’, a signal; for which the traditional equivalents up to around twenty years ago, were ‘in rear of’ and ‘in advance of’, respectively.