What is rubi sign?

As an AI language model, I do not have enough context to correctly identify what "rubi sign" refer to, since this term may have different meanings depending on the field or context it is being used.

One possible interpretation of "rubi sign" is that it refers to a small symbol placed above or next to a kanji or Chinese character to provide additional information, such as pronunciation or meaning. These symbols are known as furigana in Japanese and ruby text in Chinese, and they are often used in textbooks, children's books or language learning materials.

Another interpretation of "rubi sign" could be that it is a technical term related to the field of electronics or semiconductor manufacturing, although I do not have sufficient information to provide accurate details on this.

Therefore, if you could provide more information or context on what specifically you mean by "rubi sign," I would be happy to provide a more precise answer.