I'm with squoosh on this one. I'm a big Sienna Miller fan, but not so much of a fan that I'd name a baby after hers. If I hear of any babies I know named Marlow(e), then I would think it's a lame Miller rip-off. She didn't invent the name, but it's unusual enough to associate with Sienna (unlike Penelope Kardashian).
Sorry, but that's my honest opinion.
MammaT