In Tibetan, the om symbol is written like this:
The Aum symbol is vocalized at the beginning and end of a mantra or prayer. This beginning and end use also is symbolic of the deeper symbolism of life, from birth, living, and death.
Most people opt for a Sanskrit om tattoo, the Tibetan om tattoo is a lot less popular. Here’s a photo of a Tibetan Om with the typical clouds found in Tibetan art: