This is very interesting, I didn't know that. How did this "AH" character appear on Zong Rinpoche's skull relic and why "Ah"? Anyone knows why?
Just for your information for those who wants to know what the meaning behind "Om Ah Hum" is, here it is:
"The syllables OM AH HUM have outer, inner, and "secret" meanings. At each of these levels, however, OM stands for the body, AH for the speech, and HUM for the mind. They represent the transformative blessings of the body, speech, and mind of all the buddhas. Externally OM purifies all the negative actions committed through your body, AH through your speech, and HUM through your mind. By purifying your body, speech, and mind, OM AH HUM grants the blessing of the body, speech, and mind of the buddhas.
OM is also the essence of form, AH the essence of sound, and HUM the essence of mind. So by reciting this mantra, you are also purifying the environment, as well as yourself and all other beings within it. OM purifies all perceptions, AH all sounds, and HUM the mind, its thoughts and emotions. "
~taken from:
http://bhutanbuddhism.blogspot.com/2009/10/om-ah-hum-explained.html