Headcodes
All three locomotives were equipped with stencil headcodes, but as it quickly became apparent that suitable headcodes for freight workings did not exist (nor did the combination of two numbers only at that time, provide the scope) they were also fitted with six steam locomotive style discs at each end so that standard codes could be displayed. With standardisation came a whole set of new two-character codes with letters as well, and all three locomotives were fitted with roller-blind headcodes and the discs removed.
Read more about this topic: British Rail Class 70 (electric)