Pied markers are marks and differences on the animal's side and belly pattern and color that indicate it is carrying one of the recessive Pied genes (it takes 2 Pied genes in order for the morph to express visually, with only 1 gene they look normal). Unfortunately these marks are far from accurate and normal Ball Pythons that are NOT het for Pied can also display them.
The only way to prove that the animal is really het is to wait the years for them to reach maturity bred them and confirm the results once you see the babies. This is why you should be cautious when buying hets.
I'd recommend checking out this thread which has some info regarding Pied markers: http://ball-pythons.net/forums/showt...act-or-Fiction