Forum Moderators: phranque
What you're seeing are 12x12 pixel images to mark the end of the article, as you described. These kinds of marks can be found in print magazines, too. Some magazines just use a square, nothing fancy. Granta (litarary magazine) uses an outline of a square, flush with the right margin. So does the New York Review of Books. The Smithsonian uses a stylized circle/logo. The Atlantic magazine uses a stylized black square with a white "A", not flush right (so this is closest to what you saw online).