IP of Form submitter?

I have a newsletter sign-up form that I'm pulling stats for. I see several form submissions where the user has gone straight to the form, rather than having read an article and found the site first. I suspect we have employees filling out the form and adding people, so I was hoping to get the IP address for each form submission. I'd expect it to appear in each lead's Activity log, but I'm not seeing it there. I double click to open up the details, but still don't see it.

Is this possible? Maybe I'm just overlooking it?