Warrant canaries are used as a way for individuals or groups to give regular confirmations that everything is going well.
One prominent usecase is as a way to signalize that no government subpoena has been served to the entity using the warrant canary. By failing to refresh the canary, outsiders can be warned of a subpoena indirectly, without violating possible court orders no to do so.
This service allows any WAX account to publicly commit to a warrant canary, as well as to a deadline until which this canary is to be refreshed. This information is publicly and irreversibly stored on the WAX blockchain.