The behavior that later has been christened as sign tracking has already been noticed by the father of all the conditioning studies - Ivan Pavlov. His dogs, that were conditioned to associate a light with the presence of food, after some time started licking the light, acting as if it was the reward itself. However, busy will all the other research he had on his hand, Pavlov did not investigate this phenomenon any further. It was not until the late 60's that this kind of behavior became of interest to behaviorists and psychologists in general. Sign tracking also serves as an example of a situations where the classical and operant conditioning overlap with each other.
Sign tracking is a type of spontaneous conditioning that occurs when the Conditioned Stimulus (a light for example) starts to take place of the reinforcer itself, which arrival it is to merely announce. It is an example of autoshaping, because it occurs without a deliberate intervention of the scientist in this area. The strength of an autoshaped behavior is also an interesting matter. It will often override the originally conditioned behavior that resulted in the delivery of a reinforcer (food for example). Animals that develop a sign tracking response will continue to exercise it stubbornly, even when it clearly does not produce a reinforcer that might be needed for survival (phenomenon known as negative automaintenance).
Sign tracking can be noticed in different animal species like rats, pigeons, dogs and racoons, with some scientists looking to explore how does this affect humans: