I wasn't stuck there, but I wasn't able to find any sign of a widespread announcement. There's a Facebook event page, but it looks more geared towards attracting accomplices than spreading any coherent message to the world at large. Any such outreach seemes very limited at most--as I'd expect from a group laboring under the delusion that traffic blockages generate sympathy.
I have a daughter who lives in the City and she said most everybody knew about it a couple of days ago. She didn’t think many were going to participate but she knew about it