ways ▁are ▁given ▁al phan umeric ▁identification . ▁These ▁tax i way ▁IDs ▁are ▁shown ▁on ▁black ▁and ▁yellow ▁sign boards ▁along ▁the ▁tax i ways . ▁ ▁Sign s ▁ ▁Airport ▁guidance ▁signs ▁provide ▁direction ▁and ▁information ▁to ▁tax i ing ▁aircraft ▁and ▁air port ▁vehicles . ▁Sm aller ▁air ports ▁may ▁have ▁few ▁or ▁no ▁signs , ▁re lying ▁instead ▁on ▁air port ▁diag rams ▁and ▁charts . ▁ ▁There ▁are ▁two ▁classes ▁of ▁sign age ▁at ▁air ports , ▁with ▁several ▁types ▁of ▁each : ▁ ▁Oper ational ▁guidance ▁signs ▁ ▁Location ▁signs ▁– ▁yellow ▁on ▁black ▁background . ▁Ident ifies ▁the ▁run way ▁or ▁tax i way ▁the ▁aircraft ▁is ▁currently ▁on ▁or ▁is ▁entering . ▁D irection / Run way ▁exit ▁signs ▁– ▁black ▁on ▁yellow . ▁Ident ifies ▁the ▁intersect ing ▁tax i ways ▁the ▁aircraft ▁is ▁approaching , ▁with ▁an ▁arrow ▁indicating ▁the ▁direction ▁to ▁turn . ▁Stop ▁Bar ▁signs ▁– ▁white ▁on ▁blue ▁background . ▁The ▁design ation ▁consists ▁of ▁the ▁letter ▁S ▁followed ▁by ▁design ation ▁of ▁the ▁tax i way ▁on ▁which ▁the ▁Stop ▁Bar ▁is ▁position ed . ▁This ▁sign ▁is ▁not ▁standard . ▁Other ▁– ▁many ▁air ports ▁use ▁conventional ▁traffic ▁signs ▁such ▁as ▁stop ▁and ▁yield ▁signs ▁throughout ▁the ▁air port . ▁ ▁Mand atory ▁instruction ▁signs ▁ ▁Mand atory ▁instruction ▁signs ▁are ▁white ▁on ▁red . ▁They ▁show ▁ent ran ces ▁to ▁run ways ▁or ▁critical ▁areas . ▁Ve h icles ▁and ▁aircraft ▁are ▁required ▁to ▁stop ▁at ▁these