DECISIONS AHEAD: Roadside sign: Trailer mobile warning sign parked by road with words for safety by orange cones 24/11/2020 750 × 500 Test how well you know the Highway Code with our road safety quiz DECISIONS AHEAD: This is a photograph of a mobile roadside sign parked on highway one in northern California. It is a trailer and powered by batteries and provides information and warnings for drivers by displaying words on a large panel display.