10.- The cat doesn't want to be let out.
9.- You stop putting things in the fridge.
8.- The sitting room looks more like a bedroom.
7.- The climate control stops displaying the temperature, and just displays LO.
6.- The office greeting becomes, "isn't it cold".
5.- There are more cars with white tops than usual.
4.- You drive everywhere instead of taking the bike.
3.- Your motor bike displays an accident icon.
2.- There's no hot water cos your hot water pipe froze.

And the #1 reason you know it's cold, there's less cleavage on display around town!