Vulcan Security was an agency that operated in the Vulcan government.

In 2269, Vulcan Security was called to the home of Ambassador Sarek after he was attacked by an assassin with an Ahn-Vahr. When they arrived, they believed that Spock had suffered a breakdown after suffering from amnesia that led to the loss of his knowledge of the Vulcan mind rules and attempted to kill his own father. They were later informed that Doctor Emma Saenz was a traitor working for the Romulan Star Empire leading to Vulcan Security Central attempting to locate her. (TOS novel: Mindshadow)

Presumably, this organization was an actual body on Vulcan and was a part of the Vulcan Ministry of Security though its possible its either another name or a division of the V'Shar.