We haven't looked for any code to check for it. To do it right would require instrumenting multiple nodes in different geographic areas and connected to many different peers. Then with this information calculate a weighted order of receipt.

Once you have those stats you could score each block producer based upon how close their order was to the weighted order. Over time you would discover if there was any significant bias among block producers.

Bias alone only indicates that a producer was not well connected to the network. Once bias is discovered, then it is a matter of looking for which accounts were most frequently biased earlier. This would identify potential sock puppets.