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

Images with names like "os-upper-right-closed.gif" represent:

  "os"    - turnout with end-of-track-circuit markers in this icon.
            "turnout" - there are no end-of-track-circuit markers.
            "segment" - straight track segment
            "block", "block-end" - icons for drawing a straight block
            
  "upper" - the diverging route is above the horizontal mainline
  "right" - the diverging route goes to the right
  "closed" - the mainline is selected (c.f. "thrown" for diverging route selected)


