It's strange that Bushey station has plain station signs in the TfL Johnston font, yet no other Overground logo's (Roundels), on the platform served by LNWR stoppers. Yet Watford Junction is a mixture of signs old and new (obsolete TOCs logos covered over with duct tape, only Southern's logo remains), TfL signage on the Overground platforms, and LNWR signs elsewhere... standardised signage would be great, if now the days of franchises are over.
I don't know why there can't be a TfL style livery for the trains and whoever runs the services isn't so important It would save on all the rebranding every few years.
TfL have done that with the buses for years, ie Arriva London is in a recognisable TfL livery with Roundels and small fleetnames. Operators can still choose corporate colours for seat moquette etc...