Which data state would be most likely to use digital signatures as a security protection...

During the data-in-use state, the information has already been accessed from storage and transmitted to the service, so reliance on a technology such as digital signatures is imperative to ensure security and complement the security methods used during previous states. Data in transit relies on technologies such as TLS to encrypt network transmission of packets for security. Data at rest primarily uses encryption for stored file objects. Archived data would be the same as data at rest.