Steve, Bob, and everyone, I do not think I have ever seen 0 on a sundial, nor on a clock.
I seem to remember a sundial which had an Arabic 12 with all other numerals Roman - or was it vice versa? - but cannot think where. I would say that in England the simple cross + or cross pattee (more like the Iron Cross) is by far the most common other noon mark and at a rough guess is on 10 or 20 percent of old vertical dials; I don't recall seeing it on a horizontal dial. I can only think of two other marks for noon: at Holy Sepulchre, Holborn Viaduct, London, c 1670, there is a St Andrew's Cross X; and at Dorstone near Hay-On-Wye, Hereford, there is an interesting double sided equatorial dial dated 1823 (from memory) with what looks like a fleur-de-lys for summer noon though it is in somewhat rusty cast iron and I'm not absolutely sure how to interpret it. Andrew James N 51 04 23 W 01 17 46
