నిరోధక చిహ్నాలు (Prohibitory signs) ఒక రకమైన రహదారి చిహ్నాలు. ఇవి వాహనచోదకులపై కొన్ని రకాలైన నిషేధాజ్ఞల్ని విధిస్తాయి.
No admittance to unauthorised personnel, usually shown as a red circle with a white rectangle across its face.
Amongst one of the most familiar signs, this sign is used where parking is prohibited. Usually shown as a red diagonal inside a blue circle with a red ring in Europe and parts of Asia, and a 'P' in a red circle with a cross through in North and South America, elsewhere in Asia, Australia, Africa and Ireland.
Strictly No parking at This Site, MUTCD R7-1.
Strictly No parking at This Site, Caltrans R-28.
Strictly No parking at This Site, NYSDOT NYP1-2.
Strictly No parking at This Site, PADOT R7-7A.
Strictly No parking at This Site, NYCDOT SC-346C.
Either overtaking is prohibited for all vehicles or certain kinds of vehicles only (e.g. lorries, motorcycles, etc...) In the USA, this is usually phrased as "no passing zone" and indicated by, a rectangular, black-on-white sign on the right side of the road that says "DO NOT PASS" and/or by a solid yellow line painted on the roadway marking the left limit of traffic (centerline), and sometimes supplemented by a yellow triangular (no passing zone) sign on the opposite side of the road (where it can be seen by a driver who is attempting to pass). Conversely, when the passing restriction is lifted, a rectangular, black-on-white sign that says "PASS WITH CARE" is placed on the right side of the road and/or the yellow centerline changes from solid to broken (indicating that passing is allowed in that direction).
No right, left, or U-Turn[మార్చు]
Either for all vehicles or with some exceptions (emergency vehicles, buses). These are usually to speed up traffic through an intersection or due to street cars or other right of ways or if the intersecting road is one-way. Indicated near-universally by an arrow making the prohibited turn overlaid with a red circle with an angular line crossing it.