1) The sign seems to have been the horns (i.e. extending your index and little finger), but it's hard to be sure - but there are references to this, and to the spitting and touching iron, in various books that deal with folkways and superstitions - a good summary can be found in the Oxford Dictionary of Superstitions.
2) What I said was that I chose South Cadbury 'not because I think it the likeliest site (though I do not think it the least likely)' which is a bit convoluted, but accurate. I think South Cadbury is very likely, but so are a half dozen other hill fort sites in south-western England, and it would be almost impossible to choose between them.
3) So far as I know - Hugh-ell-bane.
4) My sources have Cadarn, yours have Gadarn, let's sort the whole thing out.
5) Derfel calls himself a pagan because he's writing late in life when he's a Christian, and anyway, lots of pagans probably assumed the label proudly, especially as it only meant 'country-dweller', so isn't a terrible insult.
6) I don't think I'll set any more books in the dark ages, unless you count the 9th century, which I'm busy writing right now.
Private (trooper in the cavalry), corporal (no lance-corporal in the Napoleonic army), sergeant (various types of sergeant, but this reply can't go on forever!). Those are the non-commissioned officers. The commissioned officers were: ensign, lieutenant, captain, major, lieutenant-colonel, colonel, brigadier general, lieutenant general, general, field-marshal.
Yes, and I'm not telling. Sorry.
I may be in Washington D.C. in the early part of next year for the American release of The Last Kingdom. Keep an eye on the Diary page as details will be posted there as soon as we receive them.