The original pictograph for the letter M was an image of water. The visual connection is obvious but the sound connection is also intriguing. M, the 13th and middle letter of the alphabet, is the deep “mmmm” my computer intones at this moment. M is the sound of machines; its consistent, steady aspect suggests the stream or river. I picture the current (liquid and/or electrical) flowing with the letter M in ripples and waves.
For the ancient Chinese, streams and rivers symbolized the mind, which never ceases flowing and is endlessly fertile. The mountain, in its vast stillness, stood as a symbol for the heart.