How to prove that during electrification through influence, the charges of body parts are opposite in sign?

Let’s connect two electroscope with a conductor and bring a charged stick to them. The leaves of the electroscope will disperse, indicating that they have a charge. Then remove the conductive jumper and remove the stick. If we now reconnect the electroscope with a conductor, the charges neutralize each other. This means that the charges of the electroscope were equal in magnitude and opposite in sign.
