New research suggests that dogs can actually remember the scents of familiar humans. The study conducted by researchers at Emory University involved using waved something that smelled like each person in front of the participating pups:
 The experiment - the first of its type - involved 12 dogs of various breeds who underwent brain scans while five different scents who placed before them.

The scent samples came from the subject itself, a dog the subject had never met, a dog that lived in the subject's household, a human the dog had never met, and a human that lived in the subject's household.

The familiar human scent samples were taken from someone else from the house other than the handlers during the experiment, so that none of the scent donors were physically present.

The results showed that all five scents elicited a similar response in parts of the dogs' brains involved in detecting smells. Responses were significantly stronger for the scents of familiar humans, followed by that of familiar dogs.
Such findings indicate that dogs respond extra strongly to the scents of familiar humans. The reaction is similar to how humans smell the perfume or cologne of someone they love, which results in an immediate, emotional reaction that's not necessarily cognitive.

[Telegraph]