There are five symbols relating to tumble drying. They’re all based on a square with a circle inside it.
‘X’ through the circle: a tumble dryer symbol with a cross through it means ‘don't tumble dry’.
Just a square with a circle: this means the item can be tumble dried, and there isn’t a specific heat setting it needs.
One dot in the circle: this means ‘tumble dry at low heat’.
Two dots in the circle: this means ‘tumble dry at medium heat’.
Three dots in the circle: this means ‘tumble dry at high heat’.