Former CFNY deejay Pete Fowler has a radio show entitled The Lost Indie City and he sells tee shirts with a big yellow 45 rpm adapter on it to promote the program. I've got one, and wear it often.
It's a fantastic conversation piece. It never fails that when I go for a walk wearing this shirt some guy, usually in his 50s or 60s, will light up and tell me he remembers those. I myself used to buy 45 singles at my local Sam the Record Man so I always had such an adapter on hand.
The other day I was wearing this shirt and walking with my wife, who was born in the 1980s and had no idea what it was, and we wondered aloud if my 14 year old would know what it was. I was pretty sure he would and my wife was pretty sure he wouldn't. My wife was right.
The 45 rpm adapter is a dog whistle that can only be heard by those of a certain vintage. By the late 80s, it was all about the CD. Even in the mid-80s, cassette tapes were taking over among my peers. I'll bet few under the age of 40 have ever touched one of these.
If you smile when you see me wearing this shirt, you're 40+. I guarantee it.