Yes, it is a mandatory legal requirement to have your luggage clearly labeled on all Eurostar trains. This is a security measure enforced by French, British, and Belgian authorities to help identify the owner of any unattended bags and to prevent security alerts that could lead to train evacuations. Every piece of luggage, including your carry-on items and larger suitcases, must have a tag that displays your full name, seat number, and destination. Eurostar provides free paper luggage tags at the check-in area and near the boarding gates if you forget your own. Beyond the legal requirement, labeling your bag is highly practical; because luggage is stored in communal racks at the end of each carriage, it is very common for passengers to have identical black suitcases. A clear, unique tag (or a colorful ribbon) helps ensure that someone else doesn't accidentally walk off with your bag at a stop like Lille or Paris Gare du Nord, saving you a massive logistical headache in a foreign country.