I've only been to a CN hiring session, but I can tell you about that.
Actually, read this
http://www.railroad.net/articles/column ... 060602.php
Its a good rundown on what it is.
One note I can give you is that they are extremely anally retentive at the railroad. Look very carefully before writing anything, because they may ask for the date in "DD/MM/YYYY" format, and if you accidentally write it in "MM/DD/YYYY" format, you are out right there. Basically they want to know you can follow orders.
The signal gangs, like MOW crews, are mostly a daytime M-F gig. You may work 1000 miles from home for months straight, but the hours are regular. You are on a systemwide signal gang that goes to a site and works on it until done , then the next. The exception to this is a derailment or mudslide or other unexpectedness that wipes out signals. You may be laid off all winter, but since you will have a notice of rehire, you can collect unemployment without searching for work elsewhere.
Train and Engine is the gig where you have no schedule.
On most roads its 2-10 years before you can win a bid on a signal maintainer position, if you bid on a godforsaken stretch of track no-one else wants, you can probably get the gig earlier than if you bid on, say, the LA area. The signal maintainer gig is where you generally get to sleep at home every night.
The upcoming PTC system should mean a lot of work for signal gangs, good luck.