An aircraft registration is a unique alphanumeric string that identifies an aircraft , in similar fashion to a licence plate on an automobile . In accordance with the Convention on International Civil Aviation all aircraft must be registered with a national authority ( such as the Federal Aviation Administration or Transport Canada ) , and furthermore , they must carry proof of this registration in the form of a legal document called a Certificate of Registration at all times when in operation . Upon registration , the aircraft receives its unique `` registration '' which must be displayed prominently on the aircraft .