The Bavli, Shabbos 21b, discusses lighting the Chanuka lights out of doors; Rashi gives the reason for outdoor lighting as
משום פרסומי ניסא / for advertising the miracle.
Further down the amud, the Bavli discusses a storekeeper who lights the Chanuka lighs outside his store. He can do so, and is not liable if flammable materials come into contact with his lamp, Rashi explains,
שברשות פירסום מצוה הניחה שם / because he had placed it there on the authority of advertising a command (mitzva).
A command? Isn't placing the lights outside advertising the miracle? What does Rashi mean here by "advertising a command", and why does he say it?