How to determine (through web crawling) if a website is using AdWords?

I'm writing a web crawler at the moment and one of the features I'd like it to have is the ability to check a page to see if a website is running PPC (AdWords). So I was initially checking for just

"googletagmanager.com/ns.html" in the HTML. As I believed it was only Adwords that used that iframe tracking, however, I believe Google analytics can also use it now.

Does anyone have any ideas?

Thanks