The charge on a glass rod which has been rubbed with silk is called positive:

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The charge on a glass rod which has been rubbed with silk is called positive by arbitrary convention. In reality, the charge on the glass rod could be either positive or negative, depending on the materials and conditions of the rubbing process. However, scientists have agreed upon a standard convention to call the charge on glass rubbed with silk positive, and the charge on rubber rubbed with fur negative. This convention is arbitrary, but it allows for standardized communication in the field of electrostatics.

The Charge on a Glass Rod Which Has Been Rubbed