All of the Runes have an image, or symbol, that sets the train of recollection, ideology, and meaning in motion. This image isn't the 'meaning' of the rune, it is the picture that sparks off of the meaning and gives it form and reality.

The prompt-symbol for As is the Ash tree, specifically the World-Tree Yggdrassill. The World-Tree has its roots in the Lower World, it's trunk in the Middle World(ours) and the crown in the Upper World. Before the invention of wards (the bumps and ridges that make a key unique) keys were smooth bars. Ash seeds look like these ancient keys and so are called keys themselves, in much the same way that maple seeds can be called helicopters today.

Ash, as the World Tree, stands for the wisdom and understanding of Spirit and the ash keys are the manifestations of that understanding being sent to us. As tells us that life-changing messages are being sent to us from the Upper World, the keys to unlocking the Mysteries of Life.