This may actually be clean but does not have to be. May sometimes forget to wear shirt altogether. If a professor is wearing blue jeans and suspenders, ten to one he is a physicist. Physics profs often have German accents, but this is not a distingushing characteristic. Be wary of psychologists with fake Viennese accents which can sound similar to the unwary.
Marine biologists walk around in hip boots for no explainable reason, even in the middle of winter.
They are apt to wear grey slacks and smell like fish, as opposed to most biologists, who smell strongly of formalin. Microbiology instructors go around in spotless white coats, refuse to drink beer on tap, and wipe all their silverware before using it. Never loan money to a bio prof, no matter how much he asks. Psychologists are not real scientists, and can be easily identified by their screams of protest whenever anyone questions whether psychology is a science. Psych people have beady little eyes and don't laugh at jokes about psychology.