The dashboard warning light showing on this page (or one very similar, sometimes a slightly different shape or colour) has appeared on the dashboard and doesn't go off when the car is running.
The engine temperature reading on the dashboard gauge is noticeably higher than usual. It doesn't seem to be caused by sitting in traffic on a hot day, it is generally just higher all the time.
On inspection underneath the car there is a puddle of coolant, the liquid is clear in colour and the texture is not like oil.
After the engine has been running there is steam coming from underneath the bonnet. The steam is white in colour.