Now to confuse you...
The spacing of signals takes multiple factors into play though so there's no hard-fast rule that says that signals should be spaced closer for curves and further apart on long stretches. There are basically two things that will determine your signal spacing, which you really need to keep watch on. The first is the speed of your trains. Trains that move quickly with little traffic will need fewer signals because they will move along quickly and there's nothing in the way to get them caught up. If you are going to run lots of traffic, then you need to place more signals because you want your drivers to always be prepared for the train ahead. On my trolley route, I have close placed signals because I have lots of trains running on that stretch of track. Think of the NYC subway system or Boston's MBTA green line trolleys as an example, which my route is more like.
For my other routes where there is frequent traffic, but not fast or complex like the trolley route, I space my signals based on the longest consist I run on that particular route. There are of course factors based on this too such as mountains, and steep grades, which require stopping distances when there is a signal on a grade for example. So to determine my longest consist, I so happened to find that 2 US Coal 3000T built-in consists, plus engines on the front, is the length of my longest train. Starting at one end of a track stretch, I put down the consist and then place my signals at the front of the train (engine end). I then slide the consist and continue placing signals until I reach the end of my line.
Also it isn't necessary to place the signals so they can be seen one after each other in close proximity. It so happened to work out that way on my route because there are a larger number of trains being a trolley system. Longer routes, as mentioned above will have them spaced further apart. My consist-measuring device really, really helps with this aspect.
Hope this isn't too confusing.
