[TBP]

How does marking the ball work?

[SAJ]

''Possibly significant'' balls are stamped with an invisible fluorescent ink, which is changed as to the composition of the ink and the pattern of the stamp with each such ball. Theoretically, one of these balls could be counterfeited, but it would be an enormously difficult undertaking.

For one thing, the would-be counterfeiter would have to have either A) the ball in question, or B) the league specs on the ink and stamp design for the ball in question. The latter is very closely guarded, you can be quite sure.