Marks and Numbers is an optional field used to identify different pieces of cargo, so that there is no problem identifying them at the port and they can be handed over to the correct parties without fail.

For example, when you are shipping two types of candles in the same container, you can mark boxes with the first type of candle with a "1" and boxes with the second type of candle with a "2".

You can then use the Marks and Numbers field to explain this to the receiving party (or parties), to help them easily identify the correct box at the destination.