UN specification cylinders were introduced in 2003. A cylinder that has been tested and satisfy the UN specification standards described in DGR 6.4, it must carry the UN specification mark shown on Table 6.4.A and explained in 188.8.131.52.2.
All previous non-UN cylinders must not carry the UN cylinder marking. They must be marked according to the rules of each individual country. Refer 184.108.40.206 and 220.127.116.11.