The reason why a formal signature should use a pen or a carbon pen is because the handwriting of the pen and the carbon pen is relatively clear, and it is difficult to be modified and erased for a long time.

Pen is a widely used writing tool, which was invented at the beginning of19th century. The pen is made of metal, and the writing is smooth, elastic and quite smooth. On the mouth of the pen or the surface of the pen tip, there are obvious trademark numbers and models.

The ink in the carbon refill is mainly composed of graphite, which is one of the most stable substances in nature. Therefore, writing with a carbon pen will not be blurred because it is kept for too long.