The two best credentials I've ever seen are, "PhD (thesis pending)", and "MA (failed)". These were both following signatures of course, not diplomas on a wall.
"MA (failed)" is pretty odd.
"PhD (thesis pending)" isn't so unusual in some form or another. Usually it's written "PhD (ABD)" for "all but dissertation," meaning they've finished all their courses and exams except for the dissertation defense. Alternately, some universities grant another degree at that stage, like an M.Phil. to avoid the seeming awkwardness of saying that you didn't finish your degree, but essentially it means the same thing.

