At Perdido, Kelly pointed out that there are colored dots on the bottom of soda cans. Different cans have different colors. I checked all the cans and they all had a dot of some color on the bottom. Even cans from the same 12-pack will have different colors. I thought there had to be a reason, but didn’t know what it might be. I did a search on Google and had the answer in minutes:
In a factory there might be several machines printing the cans and each machine prints a different color dot on the bottom of the can. This way, if there is a problem they will know which machine to shut down while the other machines continue working.