There is no special meaning to a truck being under the American flag. It can be said that a ship is under a certain flag, which means it is registered in a specific country. No such rules apply to vehicles on the road. Countries use license plates and sometimes stickers to indicate a vehicle's country of origin. So, a truck flying a US flag means the truck driver wants to express some American patriotism.
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Did you mean "holds the flag" question is confusing
danger
it means that there is no speical day that day
That the president is not home
A flag flying at the top of a lighthouse could mean several things, depending on the color and color pattern of the flag. It could mean anything from inclement weather, rough seas, hurricane, shallow water, dangerous rip currents etc.
If a black flag was flying, it meant that the play would be a tragedy
It means to be patriotic (by reference to flying the flag).
it means that there is no speical day that day
It would have meant that the British had overrun Ft. McHenry because they would take the flag down.
under flying seal
you got an antifreeze leak