Every state in America except two has laws dealing with the misuse, abuse, and desecration of flags: the American flag, the state flag, and sometimes the Confederate flag. The laws prohibit defiling, defacing, casting contempt upon, and sometimes even satirizing these flags. Most laws specify actions, but some criminalize words. A few include other venerated objects in their protections.
Wyoming is the only state that doesn't say anything about defacing, desecrating, or disparaging the flag. Alaska only bans the registration of trademarks which disparage national symbols. All other states proscribe at least some uses for national and state flags. Below are some key attributes of these laws.
Publicity: It's rarely a crime to deface, burn, or desecrate an American flag if you do so in the privacy of your home. It's only a crime to do it in public or take a flag so altered and display it in public. If the crime is the action, though, why does it have to be public? This suggests that the law exists to protect people's sensibilities rather than flags.
Outraged Sensibilities: Many laws specify that a crime only occurs if the action outrages the sensibilities of those who see or even merely learn of it. Desecrating a flag is not a crime in and of itself; it only becomes a crime when people get upset. Once again, the purpose appears to be protecting people's feelings.
Intent: Most state laws specify that flag desecration is only a crime if person intentionally or knowingly does it. If the point is to protect flags, however, why aren't there provisions for a lesser charge of negligence? Perhaps it's because the point is to suppress the communication of ideas, something that occurs when one intentionally defaces a flag but doesn't occur when one accidentally defaces a flag.
Casting Contempt: The clearest evidence that the point of a law is to suppress speech is when the crime is to "cast contempt" or otherwise "insult" the flag, such that defacing or defiling are merely examples of how the crime might occur. As the Supreme Court stated in Smith v Goguen, however, to treat something contemptuously means to express contempt, and that is undeniably the expression of attitudes or ideas which is protected by the Constitution.
By Word or Act: The most extreme examples of suppressing speech are those state laws which explicitly ban casting contempt on the flag "by word" as well as "by act." States which do this are: Iowa, Louisiana, Michigan, Mississippi, Nevada (which additionally makes it a crime to speak "evilly" about the flag), New Mexico (which prohibits insulting the flag), New York, Oklahoma, West Virginia, and Vermont. The District of Columbia used to have this, but it was removed.
Any Part: Most states define "flag" very broadly to include any part of a flag, any representation of a flag, and anything which anyone might immediately perceive as a flag. So burning a piece of a flag or a picture of a flag are crimes.
Venerated Objects: Alabama and Kentucky are the two states which connect the protection of flags with more general protections for religious objects because they classify the desecration of flags alongside desecration of churches and "venerated objects."
Advertisements: Most states ban not just defacing flags, but also using flags for advertising. This makes it illegal to sell things with flags on them (for the purpose of drawing attention) or to put ads on flags themselves. Maine, Rhode Island, and Pennsylvania only ban this and not other forms of desecration (though Pennsylvania includes things like using flags for drapery).
Personal Property: Most state laws make no distinction between personal property and the property of others; most that do say that it doesn't matter if the flag is personal property — desecration is still a crime. Only Kansas and New Hampshire ban desecration just in the context of flags that a person doesn't own.
Felony vs. Misdemeanor: Illinois is the only state to make flag desecration a felony; every other state makes it a misdemeanor. Wisconsin used to make it a felony, but the entire provision on flag desecration was struck down in 1998. Oklahoma makes it a felony to display any "red flag" or other emblem to incite disloyalty to the government.
Inciting of Violence: Maryland and Arizona are the only two states which limit the crime of flag desecration to those cases where the act might incite violence in others. This appears to acknowledge that people have a free speech right to burn or deface the flag, but then makes the person a criminal if others get so upset that they act violently in response.
Confederate Flags: Georgia, Louisiana, Mississippi, and South Carolina all protect Confederate flags on an equal basis with American and state flags. Thus burning a Confederate flag is the same crime as burning an American flag. Florida used to have similar provisions, but not anymore.