You know it's cold when .....

• Environment Canada gives out wind chill warnings
• you go outside and your boogers start to freeze
• breathing through a scarf, frost still collects on your upper lip and starts to stick to the scarf
• you sinuses start to freeze up and you get an ice cream headache
• your hands stick to the metal parts of the bird feeders
• you feel your skin starting to harden (with today's -24C and a wind chill of -40C, this can start to happen within 5 minutes)
• wet hair freezes stiff as a board
• if you breathe hard, the dry cold makes you cough
• when you come back inside, it takes five minutes for the fog to clear off your glasses
  

• fuel in your vehicle won't vaporize enough to start (petroleum vaporizes at -40C)
• fuel lines freeze
• vehicle doors freeze closed
• low temp washer fluid freezes
• you drive for 15 minutes and the vehicle interior still is freezing cold
• the drive is really bumpy because the tires froze overnight and have a flat spot
• the electrics on the vehicle act strangely
  
• the municipal trucks start using sand on the roads because salt will not work effectively
  

• wild animals are less shy, particularly if feeding
• the chickadees that already will feed from your hand are even more persistent
  
• the birds avoid the bird feeders with metal perching posts
• the cat becomes a substitute hot water bottle

One of four chickadees that come to my hand. Video pending.

• it doesn't matter how high you set thermostat, it still isn't warm enough in the house
• your find out how many clothes you can fit under your warmest coat - inside the house
  
• frost in the walls make loud, rather alarming cracking noises
• even new windows have frost on the inside
• you leave taps dripping so the lines won't freeze
• in the attic, there is frost on the nails poking through the roofing
• your hand sticks to the door handle ... on the inside!

• if you're Canadian, your reaction to this list is ....... "So?"
  

Frost on the pantry window

I'm sure there's more that could be added to the above list, but this is all that currently comes to mind from my personal experience.