OK, caveats first. It is a very very long time since I had an interview to get into the S&T, and it would have been very different then, and I wasn't coming in the way you are. Somehow I have so far avoided having to interview anybody either, so frankly what follows is my best guess, anecdote and hearsay. That said, I've been S&T for longer than I care to remember.
Of course you'll have the usual STAR competency type questions, tell us about a time you had to work under pressure etc. There's bound to be the safety vision thing too.
An obvious question is along the lines of 'what is the signalling system for' (I was asked that and I'd guess it still matters). If you have a basic idea of what interlocking, points, signals and track circuits/axle counters are that may help you.
Signalling is mostly electrical. I've heard of apprentice candidates being given a 3 pin plug and told to wire it up (doubt they'd do a practical). If you understand Ohms law that might help you.
I have heard people from PWay moaning that they went for an S&T interview and were grilled on PTS or COSS or something basic. I think I know why. Signal techs typically have a lot of courses to do and a lot of competencies to maintain, a lot more than just about everybody else. They can't and won't ask you about those because you aren't a technician yet, but they may try to assess your ability to learn and retain knowledge, perhaps from PTS pre-training or maybe something else. If a candidate doesn't know the few competencies they already hold inside out, they have little chance of keeping the details of 3 types of point machine, 4 level crossings, 3 interlockings, etc etc etc etc in their head. Sounds like you may have some kind of technical background so that might help you.
They are bound to ask questions exploring your suitability. Sounds obvious and I don't know what they'll ask but it may be worth pointing out what they'll be looking for. Signals techs tend to do a lot of shift work. Often they are the only 24/7 infrastructure staff, doing nights/earlies/lates, so they will want to know about your attitude to unsocial hours probably. Some people think it sounds like a great job until they find themselves standing around in pissing sleet at 4 am. Bear in mind that there are not a lot of indians to chiefs in signals. Typical team is operative/technican/team leader so they are not just looking for an operative. They will want someone who can progress to leading the team.
I wish I could be more help but I guess its better that the replies so far. Good luck.
