Control Panels and Signal Box Diagrams
There are many programs that can help you draw complex artwork for model railway control panels and signal box diagrams. One of the most widely available but least well known is Microsoft Word. Word has had a powerful picture drawing facility built in to it since at least Word 6.0 (circa 1994). In older versions, it used to be activated by "Insert/Object/Microsoft Word 6.0 Picture" or a similar command. In the current version you can get to it by "Insert / (Illustrations) Shapes / New Drawing Canvas".
Like most programs, it takes some time to learn most of its tricks and it has its own set of annoying "features". Some of the most useful tools are Group and Ungroup. These let you put together a composite symbol, such as a semaphore signal or switch symbol, then group them together into a single object that you can then copy and paste as needed. If you have access to an A3 printer, especially a colour one, then you can make some truly impressive panels. Another vital trick is to come up with a few basic picture elements that you really like, then copy paste and reflect them wherever needed. This particularly applies to things like diagonal lines - get the slope you want right and duplicate it so that they all end up looking consistent. If you draw each one separately, they will end up all over the place.
Here are two of my old .DOC files - a panel and a signal box diagram. They are in the old Word 6.0 format, but modern versions should be able to read them. You are welcome to experiment with them and use them as the basis for your own designs.