If one walks underneath an open ladder it is said to bring bad luck. Sometimes it is said that this can be undone by immediately walking backwards back underneath the ladder.
105
Placing a hat on the bed is, apparently, bad luck. (South Carolina)
9
Once a wedding ring has been placed on the finger, it is considered bad luck to remove it.
117
Some motorcycle enthusiasts hang a biker's bell from a portion of their bike to protect themselves from evil road spirits.
64
When you speak of bad luck, it is said that one should always knock on wood. Also knocking when speaking of good luck apparently helps with having good luck. This is an old Celtic tradition related to belief of wood spirits.
208
An acorn should be carried to bring luck and ensure a long life.
115
Two people breaking a wishbone is said to lead to good luck for the person with the larger piece.
225
Pirates believed that piercing the ears with such precious metals as silver and gold improved one's eyesight.
131