To make stock-keeping simpler and the accounts easier to work out, book signing is now a flat rate of £4 per copy.
Books in the store which previously offered 'signed' or 'unsigned' as an option no longer do, they're just the plain paperbacks. Signing is now an 'item' in its own right.
To get books signed you just add one signing item per book. If you're buying several books but don't want them all signed, you can put instructions in the 'notes to seller' field at the checkout (have faith: this box appears when you return from PayPal). Just say which books are to be signed and which are not.
The signing item now comes up as the first 'related product' on every book page, so it's easy to see.