If You Know, You Know

Every few miles along I-10 north of New Orleans you see a big billboard: head and shoulders of a long-headed, serious-looking man in a red tie, and these five letters:
IYKYK
If you squint and focus hard (IYSAFH), you can also see the name Morris Bart. If you're not driving, you can Google Bart and determine that Bart is a personal injury lawyer. Which (and I'm not saying this, I'm just saying) might conceivably explain how distracting it is to try to read the sign's fine print (there’s a bit more that I couldn’t make out to save my life) from the highway.
As for the letters IYKYK, they compose a currently popular meme. Those letters stand, if you are in the know, for "If you know, you know."
How that expression applies to a personal injury lawyer, I don't know. Perhaps Bart is appealing to people who in their heart of hearts aren't quite sure whether they have suffered a personal injury, or even have had a wreck. "Don'tcha just know it?" may be Bart's response to them, in effect.
What I do know, and know that I know, is that IYKYK fits into a significant trend. Consider:
"If you know, you know."
"You do you."
"It is what it is."
"Let go, let God."
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