I spy with my little eye

Each time I drive Donald along this road to Haddington I see a splash of blue in the hedgerow. Well today was the day to investigate what exactly these berries were. We'd located the spot (although I never glimpse them on the homeward journeys) and pulled carefully in to roughly the location putting hazards on. The car behind did not pass as we thought it would but the passenger immediately got out and came over to us to ask if everything was alright, people are kind -some, some of the time. Anyway, out I jumped with my camera. Yes, not berries at all. Graffitied with blue paint! Anyway, riddle solved.