Back before I had my own wheels, hitchhiking is how I got around. I can remember some amazing trips, like up to Cape Ann, to NYC from Lancaster PA, back to boarding school after missing the bus back from a sporting event. My parents did not approve, lectured me on the dangers, but never flat out forbid my hitchhiking. Later on, when I got my wheels, I can remember picking up a bunch of different hitchhikers, pretty much all guys, all young, all scruffy looking. Some of 'em had signs., some didn't. There would be clusters of hitchhikers at key thruway exits.
Not any more. I haven't seen a hitchhiker on a thru entrance in twenty years or more. My kids never hitchhiked. Nobody else's kids did it either. I think it has died out.
I assume the missing children on milk cartons campaign scared parents and kids enough that kids quit hitching.