Very little in the railway appears to have had proper usability testing carried out (see my rants about the TVM software) and for something as important as a sign to say what station you're at, as well as signs for the passenger to know what platform they're on etc, should ALL be standardised and not up to TOCs to change as and when to fit their corporate image.
I'm quite happy right now that they are allowed to choose, because it seems that most TOCs' sign-designing departments are less stupid than Network Rail's!