Devise a mark to represent yourself, or a name to the same
effect. Mix a drop of your own dried blood and a pinch of
your birthstone (powdered) into a paint, oil, or ink. If the mark is to
be invisible (that is, visible to those viewing with Detect Magic or
some other form of clairvoyance), you may merely draw the mark
with your finger after rubbing it in the blood & gem mixture.