According to IMDG Code 35th amendment, which is mandatory from 1st January 2012, below are the requirements for marking and placarding of limited quantities shipments.
Packages
Marking required on the package is as shown below
Top and bottom portions and line shall be black, centre area white or suitable contrasting background.
Minimum dimensions: 100 mm x 100 mm.
Minimum width of line forming diamond: 2 mm.
If the size of the package so requires, the dimension may be reduced, to be not less than 50 mm x 50 mm provided the marking remains clearly visible.
Air Shipments
Packages containing dangerous goods consigned for air transport in conformity with the provisions of Part 3, Chapter 4 of the ICAO Technical Instructions for the Safe Transport of Dangerous Goods by Air must have the marking shown below.
Minimum dimensions: 100 mm x 100 mm.
Minimum width of line forming diamond: 2 mm.
If the size of the package so requires, the dimension may be reduced, to be not less than 50 mm x 50 mm provided the marking remains clearly visible.
The marking shall be readily visible, legible and able to withstand open weather exposure without a substantial reduction in effectiveness.
Packages conforming to provisions of Part 3, Chapter 4 of the ICAO Technical Instructions for the Safe Transport of Dangerous Goods by Air is acceptable for sea transport without the need of additional markings
Containers
Containers containing only LQ shipment must not be placarded or marked but shall have below marking of size 250 mm x 250 one on each side and one on each end of the unit
Refer IMDG Code 3.5 for full details