Logos first appeared in the 19th century as the industrial revolution and printing processes gained momentum.
Up until this time products had been generally made locally and on a small scale often by hand. With the invention of machines the same products could be manufactued faster and cheaper. It was the first time products were made on a large scale in a central location and distrubuted far and wide.
For manufacturers to succeed in this newly competitive and anonymous marketplace it was important that their products could be easily differentiated, but at that time, a significant part of the population was still illiterate. The solution was to include a symbol, sign, or emblem on their products, labels and packages, so that all the buyers could easily recognize the product they wanted. Hence the birth of the modern logo!