Hell all I have to think of is how one moment Dean and Sam are wanted all over the country, their faces on the television, as massmurderers who went on a massive cross state killing spree, butchering people for no reason in diners, banks and so on...
And only a few short weeks later they can walk into a police station and no one even recognizes their face.

And it's not like either brother has the kind of face that people would just forget about...