Masonic Treasure

I think most people have heard various rumors about Masonic treasure. There have been plenty of books, movies and television, both fiction and purported non-fiction, written about the idea. However, I wanted to share with you a true treasure of Masonry which I had the honor to receive last night.

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(image property of Find by Plate)

Perhaps you've come across this cryptic code as an Internet hashtag? Or maybe you've seen it on a bumper sticker or a license plate frame? Possibly, you've seen a Mason respond with it on social media or a forum when asked how one "joins" the fraternity?

What is it?