Circular zero on oldstyle figures typefaces
On this image, you can spot the page number 209 featuring a circular zero. Many old style figures available in contemporary typefaces and fonts features a circular zero, or even a reversed weight as in Sabon + Sabon Next. Its not something new. Its how figures have to be designed since their apparition in Europe before invention of printing.
Above example is one of my image take at Cabinet des poinçons, Imprimerie Nationale in 2004, from a book printed probably by Estienne, set in a typeface who look like to be a Garamond.