I suspect most people posted outside the Supreme Court Tuesday who saw the sign knew what it meant, and thus knew without asking where Andrew Damron (the man who made it) stood on the issue.
At the same time, I suspect if someone were to ask Antonin Scalia if he knows what YOLO means, he'd fly spectacularly off the handle into full-scale, get-off-my-lawn crank mode.
I feel a little silly writing it out, but in this telling -- based on my evidence-free assumptions -- the population that doesn't know what YOLO means is a proxy for the older, whiter, segment of the population that still opposes gay marriage, still wields great political power, but all of a sudden finds itself pretty clearly out of step with the country.
That, I suspect, is why Scalia's been so contemptuous -- contemptuous, even for him -- of the fight for marriage equality. It's not just a deeply held disgust for gay people, though that's certainly a big part of it. It's that he and his cohort are losing control, and the people wresting it from them aren't just indifferent about who's gay and who isn't, but are also strange creatures from the future who seem to speak an entirely different language.