The various Oghams are used by the Irish in several ways. The Oghams were foremost an alphabet used for writing Irish. Numerous examples of boundary markers and other inscribed stones abound with people’s names written in letters from the Tree Ogham.
The Oghams have other uses as well. Some scholars think the Druids may have used them for a code language. Three Oghams often used for this purpose were the “Head in Bush”, “Head under Bush”, and “Serpent about Head”. The “Cattle Raid of Cooley” (“Ta’in Bo’ Cuailnge”) gives an instance of this. Cu’chulainn left an oak hoop with writing as a warning to the invading army. It was written in code that only Fergus mac Roi’ch, a Druid, could interpret. Fergus translated the writing this way: the army could not pass unless someone other than himself could duplicate Cu’chulainn’s feats.
In addition, several Oghams were used as mnemonic devices. For example, the Tree Ogham lists by letter - trees that are important to the Irish. Other such Oghams are “Animal”, “Bird”, “Colour”, and “River Pool” to name a few. How these worked are as follows: First Aicme, Fourth Few letter would be in English “S”. In the Oghams, “S” would be “Sionnach” (fox in Animal Ogham), or “Seg” (hawk in Bird Ogham) or “Sail” (willow in Tree Ogham).
Some of the Alphabets such as the Foot Ogham and Nose Oghams were used as sign languages. However unlike the Sign Languages of Deaf people, these Oghams were used by hearing people, as a gesture type language. This gesture alphabet could be used to communicate quickly and quietly between people. Moreover, two people could hold a secret conversation while they were speaking out loud about general topics.
Another use for the Oghams is for magical purposes. In the British Museum, there is an amber bead inscribed with magical powers. The words on the bead cannot be translated into conventional Irish. Moreover, the O’Connor family who owned this bead used it to cure eye problems. They also used it in easing childbirth.
The modern use for the Oghams is divination. Where this modern notion comes from I do not know. Perhaps, the ancient Irish did use their Oghams for divining. Neighbouring societies such as the Germans used their Runes for divination. In addition, many ancient societies thought that their alphabets had mystical properties. Also, the Irish did have myths of divine origins for their Oghams.
------, “Celtic Inscribed Stones Project”, Department of History and Institute of Archaeology, University College, London, 2000, http://www.ucl.ac.uk/archaeology/cisp/database/
Ellison, Robert (Rev), “Ogham, the Secret Language of the Druids”, Ar DraiochtFein Publishing, 2007