When I was in the Air Force, 81-86 I saw a few challenge coins, but they were few, and far between. I never had them, or received them. My former son in law is active duty USAF, and has a whole display of coins, and it seems that it is a thing now... A few week ago I was at BPS, and a vet came in and I thanked him for his service, and he asked if I served, I told him, yes, peace time in the 80's, nothing special. He shook my hand, and gave me a challenge coin (my first) I had to step back, and compose myself, it really touched me to receive one. Never underestimate what a small gesture can do for someone.