My friend is a Signalmen. I asked him the same question. He told me the Asst Signalmen will be mostly labor. He told me it's a way into the company. He did mention that UP was looking to keep the asst signalmen( errr person..sry I am not very PC) for about 7 years. I thought that sucked. He also told me you are on call. As for the interview, I can speak on that one. I just went through one for diesel electrician.
I went to the interview. The first thing I noticed was all lot of guys outside drinking coffee and no one was smoking. These guys were not there for an interview, but for some training. I went in to my room, and their was about 18 of us. They started the interview introduction promptly at 0800. First they handed us some paper work. It had some basic policies like no smoking on any company property or company functions, background check information, and a few others.
Next, they started in on how the hours can suck. We being new guys will not see a day off for a long time. We will not see weekends, ect ect. Then, they introduced the interview team and what the company is about. The interviewers were a few managers, one union representative, and a guy from human resources. Each interview will introduce them selfs. The union guy will tell you what the cost to be in the union is. The HR guy will tell you about the benefits, and then have you sign and fill out some paperwork. Finally, the HR guy will give you a time for your interview. You have to wait till then. (DO NOT SMOKE DURING THIS WAIT TIME)
When it's time for your interview, be ready. They will run behind. When it your time to go in to the room, it's like a hot seat. You have five guys looking at you and one guy asking question. Soon every person in that room will ask you a question, and some of them are redundant. You will see them writing on their pads taking notes. Be honest, look them straight in the eye. They know you are nervous, but don't LIE. I wore a white shirt, black slacks and a tie.