The manual.
I see what you’re saying, Gmail is painful to use for this exact reason. I’d argue it’s fine on cars though for a few reasons:
- there probably aren’t that many icons to be aware of in a car
- cars are generally owned for a long time, so learning 2 new icons every 5-10 years is not much to ask
- cost-cutting on I18n: the snowflake could be AC in English but “airflugencoldensteiner” in some other language. It doesn’t scale and it can’t be sold across borders without looking out of place.