A strange black cat on a porch brings prosperity to the owner. (Scottish Lore)
A black cat seen from behind portends a bad omen. (And a black cat seen from the front is a GOOD omen?)
Ahhh...an explanation here: If a black cat walks towards you, it brings good fortune, but if it walks away, it takes the good luck with it.
If a black cat crosses your path while you're driving, turn your hat around backwards and mark an X on your windshield to prevent bad luck. Oh my, what if you aren't wearing a hat? Or you're not carrying a felt-tip pen or lipstick? Please, don't try this one at home!