Korea has many superstitions but one of the most common one is the superstition of writing a person's name in red pen:
It has been said that if you write a person's name in red pen that person will die.
The reason for this is that in Korea red (especially with a red pen) means blood and stands for death. And which in this case to write someone's name in red pen is like a death wish towards that person. Or you can think of it as a death note like the anime "Death Note". The thing with the anime is that first:
• You have a book which is actually a death gods book (shinigami in Japanese) 
• And you write a persons name (regardless of the color of pen or pencil) and write the cause of death, if you don't they will simply die of a heart attack. 
But in this case it is simply with a red pen. Korean people are very superstitious about this. And if you happen to go to Korea there is a big percentage ( especially within highschools and offices ) that you won't see a red pen ANYWHERE of course they probably sell them but most likely you won't be seeing them that often.