Holly border vector comes from the book "Desk book of type specimens, borders, ornaments, brass rules and cuts: catalogue of printing machinery and printers' supplies", published in 1900 (Author: American Type Founders Company).
The holly plant is associated with Christmas in Western European culture, so at that time you can often see it in various illustrations or Christmas decorations. Very often the holly plant is represented as a wreath, which has to do with Christian symbolism. This plant is also used in heraldry, and it symbolizes truth.