Congestion Charge zone sign Near or at the start of the zone, you'll see these signs, which also say when the zone operates.
Congestion Charge advanced direction sign

On approach

Directional signs and/or road markings show which routes take you into the charging zone and which don't.

White CC marking on road

Some approach lanes to the charging zone are also marked with a white symbol. 

Congestion Charge zone sign

Within the zone

There are signs to remind you that there are cameras operating in the zone. 
Red Congestion Charge marking on road

You will often see red C road markings close to the entry of the zone.

Leaving the Congestion Charge sign

Leaving the charging zone

As you leave the congestion charging zone you'll see this sign showing the end of the zone.

Congestion Charge advanced information sign

Advance information

On the main approach roads two types of sign show hours of operation and some also show how much you have to pay.