Mini, the answers to your questions could probably fill a book. If you really want to know a lot more about signals, the best book currently out there is Railroad Signaling, by Brian Solomon. It goes into the aspects and indications displayed by signals. As always, they may differ from rulebook to rulebook, country to country, and even railroad to railroad. This should be available in a lot of the general-interest bookstores, like Border’s (that’s where mine came from a year or so ago).
Another good book with a lot of answers, probably a bit harder to find, is The Railroad–What It Is, What It Does, by the late John Armstrong. It’s a book about railroads and railroading in general, but will give good definitions of the signals, show examples of where one might run across the different aspects, and will also explain CTC in very readable terms.
For the real old-timers here, the same John Armstrong also wrote a few articles for Trains called “All about Signals”, which were later consolidated into a booklet sold by Kalmbach. That series had a very good explanation of cab signals, among other things.
“CTC Signals”. Somebody might correct me on this, but there are no such animal. CTC is Centralized Traffic Control, which is basically a set of rules by which traffic moves under the control of a dispatcher, using the same signals that you’d find under any other system.
Your fourth and fifth questions are tied together, actually. If a train is supposed to stop at a given signal, the next signal ahead of that will be an “Approach” signal, which tells the crew to be prepared to stop short of the next signal. The length of the block should be (is, in nearly every case) sufficient to permit a safe stop in any conditions.
I’d like to see Mark Hemphill jump in on this, even if he does cut me down for incorrect terminology or whatever.
Tree, in the days of semaphores, different shapes of blades had different