You know it's cold when...

... the postal carriers are wearing one-piece snowsuits.
... the moisture of your breath actually condenses on your eyelashes and freezes them shut.
... your water bottle (jostling around in your backpack mind you) actually freezes after walking outside for about 25 minutes.
... the doors of University buildings have ice--not frost, ice--solidly covering the glass.
... even the "too cool to wear scarves" people have their faces covered (only with bandanas in classic old-western style).
... the usually coveted seats by the windows of cafes and restuarants are empty and avoided.
... walking across town involves strategically planned stops to warm up (coffee shops, bookstores, post offices...).
... it's too cold to snow.