A large crowd has amassed at Union Square for today's Occupy Wall Street demonstration, and celebrities walk among them! Well, one anyway. Gawker points us to this photo of Dark Knight Rises star Anne Hathaway, holding a sign and looking mad. (And cute!) What does her sign say? Blackboards Not Bullets. (On the back is Never Trust Millionaires—especially Italian ones.)

The group of demonstrators, which includes college students who walked out of class today, plan to march down to Foley Square for a rally. Other protesters are taking their message to the subways in an attempt to persuade commuters to join them at Foley Square instead of going home to their televisions and their Seconal drips. But Parks & Rec is on tonight!

We'll update with more on the evening protests above and below ground, but one observer already notes that the NYPD seems prepared for any disruptions in the subway, at least down by Wall Street.

Update 4:20 p.m.: The "Occupy the Subway" action is underway, with protesters using the maddeningly annoying "people's mic" to harangue commuters with tales of economic woe. But not everyone's feeling it! On Twitter, one Tyler Wolf vows: "If an #OWS idiot tries to get in front of me on the Subway, I will push them in front of the train #promise." And Twitter user Misty Matonis says, "Saw a handful of #ows protestors & 3 or 4 #nypd vans at Jamaica, Queens subway/bus terminal. No real activity; riders not interested." Get your butt down there, Anne Hathaway!

Update 4:50 p.m.:amNY reports that children are leading the march down Broadway, and we're seeing reports of splinter marchers on Fifth Avenue and Sixth Avenue, where protesters have sporadically moved out in the street and blocked traffic. Estimates of the crowd size are widely varied and premature, but we're seeing unofficial estimates of at least 1,000. Down at Foley Square, another large group of protesters, comprised of many union supporters, are rallying and waiting for the Union Square marchers to reach them.

On The Other 99 live UStream, the cameraman says, "This is not an ordinary day. This protest will be talked about and remembered forever."

Update 5:15 p.m.: At least one thousand protesters are estimated in Foley Square right now, and it's crowded. Gothamist's James Thilman is on the scene; he tells us it's not quite to the point where you can't move, but with protesters from Zuccotti Park and Union Square streaming in, it's likely the square will soon reach capacity. Police are not allowing people cross the street to the park at most intersections, but Gothamist's James Thilman tells us there is one access point across from 60 Centre Street. The rally is a prelude to a march to the Brooklyn Bridge, where a line of barricades have been amassed.

(On the scene reporting from James Thilman)