This actually dates back quite a bit. We wrote about it on SEL. But I haven't seen this in the wild in a long time, and so it makes me wonder if Google is reviving this or perhaps just more advertisers are adopting it?

Either that or it is an old extension that they no longer support, but this advertiser never removed it. There's nothing in their documentation about a subscription extension, nor is the Contact Form Extension seemed to be mentioned anymore.

Apparently, the subsription form does still work though.

Weird!

Update to my blog post: I filled out the form on the ad and I was contacted by a sales person from the advertiser. Even if this is a remnant of an old extension - gives them an edge.

I believe this is an ad extension that Google has been testing for a long time.