What exactly is the point of affixing an American flag sticker to your car? Is it a memory aid for others who might be driving or walking along and have forgotten what country they’re in? ("Where are we, Denmark?" Oh, there’s the American flag on the back of a car! Thanks!") Or is it the driver’s way of saying to everyone, "I am more patriotic than you, and here’s the proof."?
Another explanation is that there’s a conspiracy of Latvians* who are plotting to take over the United States and turn it into a new Latvian homeland. The American flags are a secret signal to each other so that when the takeover begins, they know who they can trust.
Not to denigrate the symbolism of the American flag, but I do agree with the aphorism that "he who wraps himself in the flag is probably covering up something."
* – Disclaimer: I have nothing against Latvians. In fact, I’ve met several Latvians in the past and generally found them to be lovely people. I just needed to pick an unlikely nationality and "Latvian" is funnier than "Monaconian." If you are offended by this, I sincerely apologize, and suggest you substitute the nationality of your choice, such as Albanian.**
** – Second Disclaimer: I have nothing against Albanians either. In fact, I’ve also met several Albanians in the past and found them to be lovely people.