Imagine you as a guy walking behind a couple and you observed that the woman zipper is open revealing all that the man paid for. Whose attention do you call. The husband or the wife?
Same goes to a lady, if you see the same scenario with the man zipper down.Do you call the attention of the wife to it or the man himself.
Please do realize that there is no one of opposite sex that can help out
Or do you outrightly pretend as if you didn't see anything and move on?

In that kinda situation, you can look for any lady around to deliver that message to the woman, and in case there is no woman to do that, if u are bold enough to meet the man just whisper to him and if u are afraid of embarrassment look and just ignored as if you didnt see anything