On the other hand I find the article slightly dishonest on a couple of points. Not because I believe the icons are particularly obvious, but because the descriptions seem to miss the point. Here goes:
> - Ok, clock now. This is universally undestood sign that could mean literally _anything_. What time is it?
The clock is associated with time. In the context of received mail, it seems quite natural that a time-related action would be setting a reminder.
> - Right-pointing rectangle? This looks most like road sign pointing to some place, but actually means TAG. Huh?
To me this obviously looks like sticky notes you can add in books or on files to categorize content, a.k.a. quite literally tags.