Technically, it's a safety pin. This The Girl with the Dragon Tattoo international poster (full image below) is what David Fincher wanted. So far the viral internet marketing campaign, from initial leaked red band trailer to "official" green band, is as edgy as a major studio like Sony can get. While this poster will be seen in select theaters overseas, obviously this won't work stateside in print (the artful Rooney Mara as Lisbeth Salander photo spread in W has spread like wildfire).
Provocative marketing serves to get a conversation going. Women and Hollywood, for one, decries the poster as The Pornification of Lisbeth Salander. Having read the trilogy, I have no problem with this. It's the character! She's tough and sexually liberated, she wants to shock with her tattoos and piercings. Why not go there in the advertising and say, in effect, 'this is not your standard-issue Hollywood studio remake?' Now if Fincher and writer Steve Zaillian get Salander wrong in the movie, and misrepresent her relationship with her sexuality, then I will have a problem--and so will many others.
UPDATE: Here's the Swedish poster and a provocative comparison between that and the new one which makes a compelling argument. Clearly, this poster gets Salander right, while the new one leaves us questioning the American remake's take on the character.
[Hat Tip: JoBlo.]