Bricks used to have the name of the factory stamped into the clay before they were baked in the kiln. There are people who look for old buildings that are being torn down so that they can collect some of the bricks. Surprisingly, they even write books about the bricks they have found and where they originated.
What is most fascinating about these brick historians, is that they find information about the brick companies, the owners, and what other projects their bricks built. So, it's not entirely the bricks themselves that are fascinating, it's all the peripheral history that they entail.