In weather forecasting what symbol represents a 'cold front'?

Weather fronts mark the boundary between two air masses, which often have contrasting properties. For example, one air mass may be cold and dry and the other air mass may be relatively warm and moist. These differences produce a reaction in a zone known as a front.

A cold front is symbolized on a weather map as a blue line with triangles pointing in the direction of travel. The triangles can be thought of as icicles.

The presence of a cold front means that cold air is advancing and pushing underneath warmer air. This is because the cold air is 'heavier', or more dense, than the warm air. Cold air is thus replacing warm air at the surface. The tips of the 'icicles' indicate the direction of movement of the cold air.