Thanks for pointing this out. I've fixed the /mobile thing.

As to the other-- Our general policy, when we can't identify the actual author by some sort of name, whether because we can't find it or because there are half a dozen people involved, is to credit the site in general. The question hasn't come up with regard to Tumblr before, but I think crediting the posting blog is reasonable. The main reason to list the author or website is to give people a little more information before they click through.