The symbol of an "eight on its side" is sometimes known as the lemniscate and is a glyph for infinity.
The English mathematician John Wallis (1616-1703) introduced the symbol to represent mathematical infinity in his Arithmetica Infinitorum of 1655. The term lemniscate refers to the shape itself, and the Swiss mathematician Jacob Bernoulli (1654-1705) first called the shape a lemniscus (Latin for ribbon) in an article in Acta Eruditorum in 1694.
In spiritual terms, the lemniscate represents eternity, the numinous and the higher spiritual powers. The Magus, the first card in the Major Arcana of the Tarot, is often depicted with the lemniscate above his head or incorporated into a wide-brimmed hat, signifying the divine forces he is attempting to control.
The use of a figure eight to represent infinity is an interesting choice, as eight is linked to pre-creational infinity through the Ogdoad and to the cyclical sense of infinity through the eight pagan festivals of the year and the octagram.