I'm having a hard time finding the signs.  I mean, I know that I want a
white square with three parallel lines pointing downward (the "M" sign
for us) but I have to click on many of them until I find it.

Could somebody explain a bit the logic of the arrangement of signs?
Searching is taking up most of the sign-making time ...

Please feel free to point me to the documentation.  I tried to read a
lot, but I'm also eager to start writing :), so I might have skipped
something important.