A couple of generations ago, it was the custom to enclose all titles in quotation marks: titles of books, titles of poems, titles of films, titles of newspapers, and so on. This usage, however, has now largely disappeared, and the modern custom is to write most titles in italics. But in academic circles, at least, it is still usual to enclose the titles of articles in journals and magazines in quotes, as well as the titles of chapters in books — hence my reference above to Geoff Pullum's article `Punctuation and human freedom'. In British usage, however, we always use single quotes for this purpose, though American usage usually prefers double quotes here too.
It is still not exactly wrong to refer to a newspaper as `The Guardian', or to a book as `Uncle Tom's Cabin', but it is certainly old-fashioned now, and my advice is to use italics rather than quotation marks, except perhaps when you are writing by hand.