I was interested about superstitions, how 'international' they are and where do they come from. Here's some list. Feel free to add/comment.

Sign: a black cat crossing your way
Sign: you've gone somewhere and returned (forgotten something)
Meaning: (bad) Generally, bad luck on your way

Sign: a broken mirror
Sign: a bird flew in the window
Meaning: (very bad) Anticipate a deadman

Sign: whistling indoors
Sign: running water in your bathroom in your absense
Meaning: (bad) Expect the loss of money

Sign: spilled salt
Meaning: expect some quarrel

Sign: you've stepped into a pile of sh|t or a bird dropped it on you
Meaning: (good) Expect some money

Sign: dropped a knife
Meaning: (neutral) some man will come (some believe that if a fork or a spoon was dropped then a woman will come)

Sign: saw a spider
Meaning: (neutral) Expect some message

I hope this list will be continued.

As far as I know, it's considered a very bad sign in England to open an umbrella on the doorstep and placing new shoes on the table. Is it true and is there anything else?