This symbol for Deism is a classic reference to God as the Divine Watchmaker.  It is based on a writing by William Paley.

In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; I might possibly answer, that, for anything I knew to the contrary, it had lain there forever: nor would it perhaps be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; I should hardly think of the answer I had before given, that for anything I knew, the watch might have always been there. (…) There must have existed, at some time, and at some place or other, an artificer or artificers, who formed [the watch] for the purpose which we find it actually to answer; who comprehended its construction, and designed its use. (…) Every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater or more, and that in a degree which exceeds all computation.

– William Paley, Natural Theology (1802)

Paley’s argument is generally flawed.   His argument doesn’t work when applied to the creation of specific things in nature.  He was thinking about things like the design of conch shell.  By Paley’s reasoning, the complexity of a conch shell is so complex that it requires a divinity to exist.  Charles Darwin proved that that is not the case.  Paley’s Watchmaker argument does work , however, when applied to the whole of nature.  Nature requires an unnatural or pre-natural Creator.  Nature is the watch.  God is its maker.

Now, for the ultimate test, how does it look as a symbol glued onto the back of the mom mobile.

It works.

UPDATE: 
After trying on a lot of different symbols representing Deism, I finally settled on the “flaming D” you see on the top left of this page.  To see why, look here:  <http://www.amorian.org/2009/07/30/new-and-improved-deism-symbol/>

Stumble it!