So, you know how when you're playing with your toy trains, you have to follow the rules and stop at certain points and only go when it's safe? Well, when real trains are going on real tracks, there are people who make sure they follow the rules too, and those people are called railway signal engineers.
Railway signal engineers are like the train guards, but they're not on the train - they're in a special building near the tracks where they control the signals that tell the train when to stop, go slow, or go fast. They make sure that the train drivers know what's up ahead and can't go any further if there's something dangerous in the way.
The Institution of Railway Signal Engineers is a group of really smart and experienced people who work as railway signal engineers. They meet up to talk about new technology and ways to make the trains even safer, because trains are a big deal and they want to make sure everything runs smoothly.
So, basically, railway signal engineers are like grown-ups who make sure the trains are safe, and the Institution of Railway Signal Engineers is like a club where they share ideas and try to do their jobs even better.