sign on I. intransitive verb : to engage oneself for duty by signature or agreement : enlist < signed on as a member of the crew > < signed on for another six years > transitive verb : to secure the signature of : sign up : employ II. intransitive verb (-s) : to announce the start of broadcasting for the day • sign-on\ˈ ̷ ̷ ˌ ̷ ̷ \noun