The problem with the two-mode flush on toilets is that the designer is trying to be subtle in communicating "do this for urine, this for feces." If we wanted to

The problem with the two-mode flush on toilets is that the designer is trying to be subtle in communicating "do this for urine, this for feces." If we wanted to be explicit, one button would be brown and log-shaped and one would be yellow and drop-shaped. We don't want to be crude, so we instead have more cryptic symbols.