On several other iPod/iPhone sites I've visited, in your profile there is a "device" field where you can select which model of iPhone/iPod Touch you have and this info appears on the left of each post under your avatar.
I know this could be put into your signature, but its such a small piece of text that it'd be nice if it could appear with your avatar.
I'm not sure the capacity is nec, so you could put something like:
iPod Touch 2G
iPod Touch 3G
Just a thought.