Canned food has rings stamped on the lids. What (or who) has the code? Here is a photo with crab and tuna tops. Maybe the better word would be "indentations"?  
There’s no hidden code in the rings, they are just there to stabilize the thin metal. A flat sheet is weaker and more flexible than one with ridges - the same reason why roof and wall metal is usually corrugated. On taller cans you will often also find corrugated areas on the sides of the can, hidden by the paper label. 