Interpunct illustrated and explained

"An interpunct ( · ) is a small dot used for interword separation in ancient Latin script, being perhaps the first consistent visual representation of word boundaries in written language. The dot is vertically centered, e.g. "DONA·EIS·REQVIEM", and is therefore also called a middle dot or centered dot. In addition to the round dot form, inscriptions sometimes use a small equilateral triangle for the interpunct, pointing either up or down. Such triangles can be found on inscriptions on buildings in the twentieth century. Ancient Greek, by contrast, had not developed interpuncts; all the letters ran together…The use of spaces for word separation didn't appear until much later, some time between 600 and 800 AD."

Much more at the Wiki link re its use in other languages, computer code, etc. Upper image credit to jrwebbe's Flickr photostream. Lower image credit to Painintheenglish.com, where in the discussion it was noted that the use of the interpunct for this NYC railway sign makes it easier for the reader to see Prince St. rather than "Princest" with perhaps the intention of avoiding any hint of an offensive word...