What is this wire connected to the back of my radio?

I’m hoping to replace the radio in my ’05 Saturn Ion, so I pulled it out to see what connections it has. According to this website, this radio is compatible. I know I’ll have to deal with the wiring harness, but that’s not a big deal. However, there’s one wire on the current radio that is separate from the big connector and I’m not sure what it is. I did some googling but couldn’t find this particular model of radio (I might not have found the right serial number) and also couldn’t find any other radios with anything similar.

Picture of wire:

The gold connector slides over this tab:

Any ideas as to what this wire is? And do I need to look for a radio that has that particular attachment, or can I safely ignore it?