Apparently, and I'm not sure, but you have to be a premium member now to have an image in your signature. Sigs are also limited to 50 characters per line if you're not a premium member.
The sig I have below turned into a URL until I ponied up $12 for the year. I figured I appreciate this site enough for $12.
It would have been nice to see some sort of announcement though, I don't recall one.