There is a tattoo on the arm of Hazen Kaine, played by Dominic Purcell. The sign has a very important role in the plot of the film. In reality it is based on the Pliska Rosette - a seven-pointed bronze rosette with a type of runic letters and signs on it found in 1961 in Pliska, the medieval capital of Bulgaria. It is dated by archaeologists to the VII-IX century. The plot of the film also takes place in Bulgaria.
The kings mentioned in the film: Kardem and Trevin, including his alter ego Ayavlo are most probably named after three Bulgarian kings: Kardam and Tervel, who led the First Bulgarian Empire in the VIII century and Ivaylo, who was a XIII century ruler of the Second Bulgarian Empire, respectively.