How do Ancestral Seals work?
The Ancestral Seal is an item required to upgrade a Level 10 building to Level 11 or higher. Much like the Completion Grant, once used this Item will disappear from your Inventory.
To use this item, simply click your Level 10 building and select the "Upgrade" option. Check you have met resource requirements as well.
You may purchase the Ancestral Seal in the Shop under the General tab.