Sienna Miller quietly voiced her support for gay marriage when she went for a stroll with baby Marlowe in NYC on Saturday. She attached a logo sticker from the Human Rights Campaign, a LGBT equality-rights advocacy group, on the front of her baby carriage. It's the same logo that inspired many Facebook users to "go red" in late March while the Supreme Court held a hearing on gay-marriage laws. Aside from supporting marriage equality, Sienna has been laying low in the Big Apple over the past couple of weeks, while her boyfriend Tom Sturridge works on his new play, Orphans. The production, which also costars Alec Baldwin and Ben Foster, recently went into previews and will officially open on April 18.