Happy Birthday, John!
I didn't even know that Flag Day was a thing
That may be because most other countries don't have the same relationship with their flag, nor does their flag have the same symbolic meanings.
For most countries, their flag is their banner to rally around and represents their country. All good for sure.
But for the US flag, white signifies purity and innocence. Red, hardiness & valor, and blue signifies vigilance, perseverance & justice. And of course the stars represent the states, and the flag as a whole, represents freedom the world around.
Everything about the US flag has significance. There are 13 stripes for the original colonies. Even the 5-pointed stars (chosen by Betsy Ross) represents America's military might.
If you discount changing the number of stars, not many countries have national flags that have gone unchanged for so long.
Sorry, John, for running your birthday wishes thread so off topic. Clearly you should have been born in July!