Ogham

The Celtic Ogham (pr: Oh-yam) alphabet dates from the fourth century. The alphabet is named for Ogmos, the Celtic god of knowledge and communication. Ogmos was associated with the Gaulish god Ogmios, and the Greek Hermes.

The ogham alphabet has twenty letters, each named for a different tree sacred to the Celtic Druids. Each letter is made up of one to five straight or angled lines incised on a straight base line. Because the number of letters, and the number of lines that make up each letter, some scholars have theorized that the ogham may have originated as a system of hand signs, likely a system of communication used by the Bard class.

Examples of Ogham writing have been found all over the British Isles, and even as far away as Spain and Portugal. All surviving examples exist as stone carvings, usually on tombstones and road markers. Although it is commonly used by modern Druids and other NeoPagans as a divination system, there is no real relationship between modern and historical divination systems.
When used as a divination method, the letters are usually notched into straight twigs and used much like runes. To see the entire Ogham alphabet and download a set of Ogham cards, see:  The Celtic Oracular Alphabet