A certain kind of Google Ad uses John Hudson’s size-specific design Slabo. Slabo is interesting because it comes in two very uncommon optical sizes – 13 and 27 pixels, respectively.
There is not a lot of information to be found about Slabo, except the description on Google Fonts, which suggests there may be other optical sizes forthcoming:
Slabo is a collection of size-specific fonts for use in online advertising and other web uses. The collection currently includes […] Slabo 13px, and Slabo 27px. Each font in the collection is fine-tuned for use at the pixel size in its name.
I doubt any of the ads collected use Slabo at either 13 or 27 pixels – however, knowing this constraint helps understand some of the design’s idiosyncrasies.
It would be educational to see a specimen of the typeface in its intended environment, or read some of the decisions that went into making the design. For now, the description on Slabo’s Github repository is mainly concerned with font production, while users try explaining the design in their own way.