Is it a racial code? Not exactly.
It is, however, a class code.
The point of the "pick-up truck" is for Scott Brown to identify himself with blue collar workers, despite not being a blue collar worker himself. Yes, he is primarily trying to be identified with working class whites, but his interest is more in being identified as their champion vis a vis snobbish white collar sorts (which is the implication that is desired whenever the term "liberal elite" is used). Put another way, he is saying "I may be white collar, but I have blue roots."
This is also the tack used with Sarah Palin, and at least in her case, I found it rather grating (and to the extent that Scott Brown played the same cards as Palin, found it grating for him as well). This is not because I have anything against blue collar workers, or think that they are not capable of being politicians. What I find grating is the constant emphasis on this identification rather than on the actual issues.
I will admit that I have not followed enough of Scott Brown's campaign to know how much he talked about actual issues. I am under the impression that he did so enough to be a reasonable candidate.
The problem with Palin, however, is that her identity and her life seemed to overwhelm any particular ideas she had, and those who swooned at her did so for identity politics reasons rather than due to any actual issues.
In this way, Palin was in many ways similar to Obama, and those who mock him as the "Obamessiah" should be careful (as many have not been) not to venerate Palin in exactly the same way.
That is all.