A  C  B  G  B  G  G  B  B  G  B  G  Figure 14-26.  Holding position marking on a taxiway.  Figure 14-27. (A) Yellow “X” placed on surface of temporarily closed  runways. (B) Lighted “X” placed on temporarily closed runways.  (C) Lighted “X” at night showing a temporarily closed runway.  Figure 14-27A  shows an example of a yellow “X” laid flat  with an adequate number of heavy sand bags to keep the  wind from getting under and displacing the vinyl material.  A very effective and preferable visual aid to depict temporary  closure is the lighted “X” placed on or near the runway  designation numbers.  [Figure 14-27B  and  C]  This device is  much more discernible to approaching aircraft than the other  materials described above.  Some other markings found on the airport include vehicle  roadway markings, VOR receiver checkpoint markings, and  non-movement area boundary markings.  There are six types of signs that may be found at airports. The  more complex the layout of an airport, the more important  the signs become to pilots. Appendix C of this publication  shows examples of some signs that are found at most airports,  their purpose, and appropriate pilot action. The six types of  signs are:  14-15  • Location signs—black with yellow inscription and a  yellow border, no arrows. They are used to identify a  taxiway or runway location, to identify the boundary  of the runway, or identify an instrument landing  system (ILS) critical area.  • Mandatory instruction signs—red background with  white inscription. These signs denote an entrance to a  runway, critical area, or prohibited area.  Airport Signs  Other Markings  Temporarily Closed Runways and Taxiways  For temporarily closed runways and taxiways, a visual  indication is often provided with yellow “Xs” or raised  lighted yellow “Xs” placed at each end of the runway.  Depending on the reason for the closure, duration of closure,  airfield configuration, and the existence and the hours of  operation of an ATC tower, a visual indication may not be  present. As discussed previously in the chapter, you must  always check NOTAMs and ATIS for runway and taxiway  closure information. 