Writing names in red ink is a superstition. Writing names in red ink meant death penalty in ancient times, but the reason why people taboo writing names in red ink is mainly because people sentenced to death in ancient times will write their names on their betting numbers with chicken blood, so there is a saying that "Dan Shu is ominous". Besides, writing a letter with a red pen means breaking off diplomatic relations.
The saying that extended information is written in red ink:
Writing names in red ink is actually a taboo rather than a superstition. The reason for this taboo is that the name of the criminal should be written in striking red, and the most striking red is also used in the inscription. So writing other people's names in red ink really gives people a rude feeling. There is nothing superstitious in it, and at that time, writing letters was only used in an emergency, and cinnabar was also used at that time. Now, it actually means celebration and blessing.
Another reason is probably because the emperor generally used a red pen to approve the passbook. Of course, ordinary people can't write in the same color as the emperor. At that time, the emperor was in charge of the world and only he could use it. So for these two reasons, it is not allowed to write other people's names in red pen in China. Although there are different opinions, these two have a long history.