You are may be wondering if its really illegal to copy or duplicate a key with a Do not duplicate message on it but, its actually not and locksmiths can duplicate these for you unless, the key is part of a patented/restricted key control system, or the locksmith suspects wrongful intent.
The engraved message found on many business keys are not legally binding its just a recommendation. Though many chain hardware stores may refuse to cut a copy of these keys, but a locksmith can easily duplicate them.
Property owners and managers began pressing the do not duplicate key message to control security violations from terminated employees, former tenants, construction workers and others who gain possession of a key. Unauthorized key duplication remains a serious threat to security today and is currently the single most violated security policy in business.
The inscription may lessen the number of copies in circulation because of the need to have them copied by a locksmith. Yet the fact remains that keys stamped with this message are no more secure than keys without it.
If you need an effective security you should get a patented key control system rather than relying on a key with a simple marking. This does not apply to keys protected by law.