Generally speaking, if there is a signature, it is signed on the label inside the piano box. Because the signature can easily hurt the violin (violin is a precision instrument, even a slight injury will cause problems). Secondly, if it is written in, it will wear and fade in a short time.
Violin signature: Generally speaking, the body label will include brand, year, serial number (some handmade violin workshops may not have it), pianist (some handmade violins may have it), size and so on. Generally, hand-made violins are labeled with an internal standard, which is one of the main symbols of the violin, just like a person's ID card.