When you don't have a helmet lock and need to leave your motorcycle helmet behind while entering a building, you have a few options:
Take it with you: Carrying your helmet with you is the safest option. It ensures that your helmet remains secure and avoids the risk of it being tampered with or stolen. You can hold it in your hand, use a helmet bag, or attach it to a backpack or other carrying device.
Store it in a secure place: If the building you're entering has a designated area for helmet storage, such as a locker room or a coat check, you can inquire if they allow helmets to be stored there. Make sure it is a secure location with controlled access and that you receive a ticket or some form of verification for retrieval later.
Lock it to your motorcycle: While you mentioned not having a helmet lock, it's worth considering investing in one. Helmet locks are affordable and easy to install, providing a secure way to fasten your helmet to your bike. Alternatively, you may be able to use a sturdy cable lock or combination lock to secure your helmet to the motorcycle's frame or other secure parts.
Remember, leaving your helmet unattended with your motorcycle carries the risk of theft or vandalism. It's always advisable to take your helmet with you or find a secure storage option to ensure its safety.