Butchers are commonly seen in a navy blue apron with white stripes. Wearing of the "livery" or uniform was compulsory if you were a member of The Butcher's Guild, an association of butchers in the UK which began in the 10th century and still exists today.
An apron with a single large white stripe means you are a butcher that has done the hard yards (ie "earnt his stripes") by himself. An apron with a big stripe and a little stripe means you are a butcher that has been trained via an apprenticeship. Apprentices wear aprons with thin,narrow stripes until they qualify.