You used to be able to get (and may still be able to ...), from a local aviation supplies shop, a small 'winged' lapel badge which says 'Mile High Club' on it.
Many, many years ago a friend was explaining how he spent his honeymoon in Denver in Colorado. They didn't have much money, so one of their wedding gifts was a trip to Denver and stay with some family friends. I remembered that Denver was known as the 'Mile High city', so I bought him one of the badges, and he still wears it on one of his jackets.
He says that it is noticed by quite a few people, and they act surprised and impressed when they see it.
As I only got 1 badge, every time I see his wife, she always says to me "where's my badge?"