Never write someone's name in red. For obvious reasons the color is synonymous with blood, and it is considered a bad omen. Many new teachers make this mistake when grading students' homework.
The number 4 is considered unlucky. This is because the pronunciation for the word "4" is very similar to the pronunciation of the word "death" For this reason some buildings will omit labeling the fourth floor, preferring to skip from three to five instead.