They get a splotchy reddish coloration on their chests, sometimes spreading to their throats... on some women it only lasts a minute... on others it may linger for 20 minutes or more...


Like when someone is embarrassed and they "blush"?
Like that, but on their upper chest/neck area.

This is the only ironclad physical sign of orgasm in women.
While not ALL women show this sign... it is visible in the vast majority.