The Flag Code, which formalizes and unifies the traditional ways in which we give respect to the flag, also contains specific instructions on how the flag is not to be used. They are:

The flag should never be dipped to any person or thing. It is flown upside down only as a distress signal.
The flag should not be used as a drapery, or for covering a speakers desk, draping a platform, or for any decoration in general. Bunting of blue, white and red stripes is available for these purposes. The blue stripe of the bunting should be on the top.
The flag should never be used for any advertising purpose. It should not be embroidered, printed or otherwise impressed on such articles as cushions, handkerchiefs, napkins, boxes, or anything intended to be discarded after temporary use. Advertising signs should not be attached to the staff or halyard
The flag should not be used as part of a costume or athletic uniform, except that a flag patch may be used on the uniform of military personnel, fireman, policeman and members of patriotic organizations.
The flag should never have placed on it, or attached to it, any mark, insignia, letter, word, number, figure, or drawing of any kind.
The flag should never be used as a receptacle for receiving, holding, carrying, or delivering anything.

Read more here:
Flag Etiquette