- Live Fearlessly, Compassionately and Honestly
 
"Om has only a mystical meaning — suggesting primordial reality. Mani means jewel, while Padme means lotus. Hum, like Om, has no conceptual meaning. Overall, the mantra is suggestive of the bringing together of the qualities of wisdom (the lotus) and compassion (the jewel).

Just as the lotus can exist in muddy water without being soiled, so wisdom can exist in an impure world without becoming contaminated.

And the Dalai Lama points out that just as a jewel can relieve poverty, so the compassionate mind takes away the poverty of unhappiness that exists in the world and replaces it with the wealth of wellbeing." source: 
http://www.wildmind.org/mantras/figures/avalokitesvara
Picture
I got this on the Everest Trek in Nepal. It reads: Om mani padme hum.
"Tibetan Buddhists believe that saying the mantra (prayer), Om Mani Padme Hum, out loud or silently to oneself, invokes the powerful benevolent attention and blessings of Chenrezig, the embodiment of compassion. Viewing the written form of the mantra is said to have the same effect -- it is often carved into stones, like the one pictured above, and placed where people can see them." source: http://www.dharma-haven.org/tibetan/meaning-of-om-mani-padme-hung.htm
The Mantra Om Mani Padme Hum

The Mani mantra is the most widely used of all Buddhist mantras, and open to anyone who feels inspired to practice it -- it does not require prior initiation by a lama (meditation master). The six syllables of the mantra, as it is often pronounced by Tibetans -- Om Mani Padme Hum -- are here written in the Tibetan alphabet reading from left to right the syllables are:


         Om (ohm)  Ma (mah)  Ni (nee) Pad (pahd)  Me (may)  Hum (hum)

The vowel in the sylable Hu (is pronounced as in the English word 'book'.) The final consonant in that syllable is often pronounced 'ng' as in 'song' -- Om Mani Padme Hung. There is one further complication: The syllable Pad is pronounced Pe (peh) by many Tibetans: Om Mani Peme Hung.