Thanks ameribbean expat.
Barry Fell noted that a figure on the Gundestrup Cauldron is holding up his hands and spelling "thunder" in Ogham and the figure is a thunder deity (later known as Thor, basically). One view (which IMHO is correct) is that the method of writing began as fingerspelling, a way to communicate silently and (if others were unfamiliar with it) secretly.
Great story. Thanks.