Excerpt from the U.S. Flag Code.
The flag should not be used as "wearing apparel, bedding, or drapery", or for covering a speaker's desk, draping a platform, or for any decoration in general (exception for coffins).
The flag should never be drawn back or bunched up in any way. The flag should never be used as a covering for a ceiling.The flag should never be fastened, displayed, used, or stored in such a manner as to permit it to be easily torn, soiled, or damaged in any way.
When the flag is displayed on a motorcar, the staff shall be fixed firmly to the chassis or clamped to the right fender.