Mina symbolizes the ideal Victorian woman. Her story in Dracula also includes symbolism relating to sexuality and purity, and the mark on her forehead signifies her "unclean" state after being bitten by Dracula.
Harker decides to strike Dracula with a shovel to liberate the world from life-threatening vampires. Just at the moment before he strikes Dracula, Dracula's eyes stare in horror and fear at Harker. Dracula's eye movement scared the beans out of Harker causing him to drop the shovel on Dracula's forehead leaving a scar.