Dumb? That is a major question for archtectural historians and for craftsmen working on reconstructing old buildings.
Reclaiming and cleaning up old bricks for re-use on conservation and reconstruction projects is a million-pound business in UK alone. It's an important part of the building materials business.
Copying old bricks to make new ones like old ones were made is also big business and includes making modern copies of Roman bricks from two thousand years ago.
Be broken hearted not..look at buildings and compare your brick with other bricks.
Some bricks can be easily identified.
Only a few brickworks were in existence many years ago, close to the raw materials the bricks were made from, so identifying bricks isn't always very difficult because materials methods and designs were different in different brickyards.
The economics of scale meant that small brickyards couldn't compete with the big ones unless they were making unique styles of bricks or had a local transport or some other advantage.
Red or brown, grey or yellow bricks, bricks of specific sizes and with holes or depressions of a particular character can be traced to particular brickyards and dates.
Here's the good news...err, the bad news...no, the good news
10 100 000 sites. Shows how important it is.
Add UK to the search terms and you get 3.600 000 sites, including brick identification charts and descriptions.
Cut's it down a bit eh?
http://www.google.com/search?hl=en&q=identifying+house+bricks+history
Have fun