An urban guerilla would be fun. Scarf, hooded top, jeans or combats, pistol, molotov.
I second that, provided that you distinguish between protesters and urban guerillas.
I don't know much that you don't know about urban guerillas, so I'll reserve comment.
But I do know that we don't have any modern protesters in the database, but we do have riot police units. So sad...
I agree with Quinzy about the basics: Dark clothing, combat boots, scarves (they like black & white, but there is no "look", save that european protesters prefer scarves with fringe), hooded tops sometimes, and backpacks are common. I've never seen them use guns, but Molotov Cocktails have been a popular means of communication at World Economic Cabal meetings. I propose that it should be an M-Unit of 3 or more, since the very idea is that it's a mob - and a Protesters M-unit would be easier to match up against police, strength-wise. Just
one protester would only be annoying, mistaken for an anarchist, arrested for impersonating a college student, and beat to a pulp.
This popped up and I had to link to it. I have no idea what the story behind it is.
This one's fun, obviously the fairer sex, and the steampunk goggles are a great touch.
Time Magazine's Protester: person-of-the-year 2011.
Quebec protester with knapsack
Here's Another from Chicago.