TPPhotog has a great point about consistancy. It's great if YOU know what you mean with whatever sign you use. However, as has been pointed out, the colon is open to interpretation. Maybe I'll be in the minority, but I'm sticking with the "+" sign. With that one there's no doubt. It will always mean x+y=z. But then I've always said "passenger side " or "driver's side". The left or right front of the car isn't accurate enough and depends where you are standing.