On mobile, the ads I see are almost exclusively fake virus warnings, "clean your phone" and other crap like that. Complete with flashing yellow and red images.
Are those Google Ads though? Google is indeed a dominant player in the advertising market, but they're not the only one. You could be seeing ads from a different ad network.
All of those things you described (fake virus warnings, "clean your phone", flashing yellow and red images) are against Google's policies for AdWords. See:
> we disabled more than 5 million payday loan ads
> In 2016, our systems detected and disabled a total of 112 million ads for “trick to click,” 6X more than in 2015.
> We disabled more than 68 million bad ads for healthcare violations, up from 12.5 million in 2015.
> We took down more than 17 million bad ads for illegal gambling violations in 2016.
> In 2016, we took down nearly 80 million bad ads for deceiving, misleading and shocking users.
> in 2016, our systems detected and disabled more than 23,000 self-clicking ads on our platforms, a huge increase year over year.
> Last year, we took down almost 7 million bad ads for intentionally attempting to trick our detection systems.
> In 2016, we suspended more than 1,300 accounts for tabloid cloaking.
> We took action on 47,000 sites for promoting content and products related to weight-loss scams.
> We took action on more than 15,000 sites for unwanted software and disabled 900,000 ads for containing malware.'
> And we suspended around 6,000 sites and 6,000 accounts for attempting to advertise counterfeit goods, like imitation designer watches.
[1]: https://blog.google/topics/ads/how-we-fought-bad-ads-sites-a...