Public domain
In some cases, if a work enters the public domain after copyright expiration, anyone using the work may still be required to note who created the work.  Even if some works are in the public domain due to not being copyrighted, there may be still non-copyright usage restrictions. For examples, even though the design of national currencies may be ineligible, or be unsuitable, for copyright, counterfeiting them for fraud is widely a very serious crime. Another example are logos and images that only have text or simple shapes. These logos aren't copyrighted in the United States, but they are often protected by trademarks.