Under European Regulation (EC) No. 1935/2004, when you buy a mug, or any other product that comes into contact with food, and that the latter is intended directly for the end consumer, you are required to include the following information on the item itself (either directly, or via the label, the packaging or on a sign placed near the items):
The object's reference or model
The glass-fork symbol or the words "Suitable for food"
Name or company name, and, in all cases, the registered office address of the seller responsible for placing on the market
Batch number enabling traceability to the end customer