Noticed something walking through the airport today. The signs that warn you (wet floor, do not enter, emergency exit) almost universally use sans-serif type. Usually bold. Usually uppercase. Helvetica, or something close to it.
But the signs that inform you (gate numbers, baggage claim, ground transportation) are often set in a lighter weight. Sometimes with serifs. Sometimes mixed case.
We've collectively decided that danger sounds like a shout and information sounds like a conversation. That's a design decision embedded so deeply in our built environment that we don't even notice it anymore.
I wonder when that convention solidified. Was there a moment when someone decided that serif type was too gentle for an emergency? Or did it emerge naturally, the way desire paths form across lawns?
Next time you're in a public space, look at the hierarchy of urgency in the signage. The typography tells you everything about what the designer feared you might miss.