"Priory of Sion" in Portland OR

In Portland OR, I saw the following chalked on sidewalks in different parts of the city: PofS, with boot

 

PofS, slant

In one or two cases, there was more of a message but we were typically walking too fast (even on vacation, we hurry hurry hurry) for me to read it or take a picture.

So, two questions leapt to mind.

What the hell is the Priory of Sion?

The Priory of Sion is a well-known secret-society hoax, according to Wikipedia, itself a secret society in some ways, but never mind that now. The world has Dan Brown’s novel The Da Vinci Code to thank for promoting the Priory of Sion to a higher profile. Google will lead you to many other sites.

Why is Priory of Sion appearing all over the streets of Portland?

That other conspiratorial place, Reddit, had a few threads, like this one, on the phenomenon. One of the posters sees this as the work of one person who has a history of posting messages all over town, and others responded saying they’d seen different guys chalking the sign on the sidewalk.

What does a society have to do to stay secret??