Ancient talisman is a quest item. It is obtained and used in The Dig Site quest. Once you have passed all exams, go to dig in level 3 site (requires trowel and specimen brush) and you will eventually find the ancient talisman. Bring it to the archaeology expert to learn that it is actually a talisman of Zaros. The archaeology expert is impressed and will give you an invitation letter to enter winches.
The talisman's inscription reads: "Zaros will return, And wreak his vengeance upon Zamorak the pretender."
After the quest, the talisman is on display at the Varrock Museum.