Social signalling is relative to the things available for that society. Even if there were no "nice cars" available by your standards, there still were "impressive" cars, relative to the society in question.
(And in any case, the range of cars available was much more compressed. Thus there was less differentiation at the high range.)
The big brass were driving Volvos. They were nice cars, but Sweden was seen as sufficiently neutral and socialist-like.