My recent experience, although not with signs, is that charging VAT is no longer patchy. Things have been tightened up, and HMRC charges VAT on everything including postage and insurance, over £18 in value. If the item is an antique, (and was made in this country originally?) VAT is currently charged at 5%, but you have to first pay the VAT at 17.5%, and subsequently claim back the difference between 17.5% and 5% VAT rates! (It seems a bit of a minefield, and I'd suggest anyone should look at the HMRC website for details.)