what does it mean when the American flag is upside down?

Nation in peril. They should all be upside down at this point.

"The upside down U.S. flag is an official signal of distress."

[link to www.jeffhead.com]

A recently divorced woman lives across the street, and her husband had been a Marine for a number of years. One morning as I went across the street to the mailbox to get the paper, I noticed that there was an American flag hanging upside-down on her garage. I went running up to her front door and started ringing the doorbell and banging on the door until she finally answered it. I had obviously rousted her out of bed, but I asked her about the flag and she came outside to look at it (like maybe she thought I was just raising a ruckus for no reason!) Well, turns out her teen-aged kids had had a party the night before, and obviously someone thought it would be cool to hang up the flag (not even sure if they knew that it was upside-down considering how they teach kids in school nowadays). She wasn't even aware that it was the universal sign for "Something's wrong - come quick!" until I explained it to her, and that I'd been worried that she was in danger or distress so I'd come right away to check on her situation. That's what good neighbors do. Probably a good thing that I didn't have my rifle with me or she'd have thought I flipped out for sure!!

It means you're standing on your head.

You are a good neighbor.

OP--people use the upside down flag to express their views that the nation is "wrong" in their view. But it is a distress signal--a call for help.

I passed an upside down flag in an apartment window. My first thought was to call the police and have them do a safety check--and I should have because it could have been an elderly person without a phone who fell ill or a hostage situation. But I assumed it was just some mentally ill hippy expressing his discontent. I hope I wasn't wrong.