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You can use CSS expressions to do this. For example you could plug a ♣ symbol via:
expression(this.runtimeStyle.backgroundImage="none",this.innerHTML = '♣'+this.innerHTML)
I wrote an article about this on Smashing Magazine, see http://coding.smashingmagazine.com/2011/03/19/styling-elements-with-glyphs-sprites-and-pseudo-elements/