TESA is a company that makes electronic security locks/entry systems for hotels, or anyone who has a need for secure doors. They provide these "generic" keys to use as backups, should a company run short of their regular keys. Sometimes these generic keys are all that a hotel might use, so that if a person lost his/her key, the finder would not be able to determine where their room was.

I have found that women travelling alone will sometimes ask if we can issue them a key without the hotel name, address or phone number on it.