I'm not sure I understand the question.
If you're asking if (in a 12V circuit) "would +12V be logic high and 0V be logic low?" then the answer is: "Probably, maybe". Much logic operates at lower voltages (5V, 3.3V) and applying 12V to their inputs may be a very bad thing. In general, 0V is logic low and the logic supply rail is logic high.
I'm not sure where you're going with the former part of the question, or its relevance to the second.