Centurions were made by a number of different manufacturers, so it could be just about anywhere. In addition to the traditional BB shell placement, check the bottom of the seat tube, around the front derailleur. This was fairly common on earlier models. Also check the rear dropouts, head lugs and top of the seat tube. If you still can't find any, the head badge style will at least allow us to establish an era.
If you're looking for an ID you'll have to post pics so we figure out the model/level, so you might as well post pics of the headbadge.