These icons were extracted from images on Carsten S. Lundsten's web site.
Please see http://www.lundsten.dk/us_signaling/abs_st_sp/index.html#example

Directories are:

  track-segments:  A set of icons for drawing track segments.  These
                   have a medium-gray background
                   
  searchlights:    Seachlight signals for a track diagram.
  
  aspects:  displays of various signal aspects, organized by analogy
            to the aspect signaling definition directories
