They give thumbs up, but in some areas, especially inland areas, they don't do this, but get in the way.
In fact, the correct sliding posture is to stretch out your arms and give a thumbs up. The right picture is the correct sliding gesture!
They held out their forefingers and pointed their hands away.
Cars. In some parts of India, they waved to cars. In some parts of Africa, their palms always face up. In Israel, the signal of hitchhiking is the road pointed by fist and forefinger. Hitchhikers can also carry a sign showing their destination and/or language.
In order to improve the success rate, hitchhikers need to smile to prove that they are friendly. Of course, you can also spend some money to pay the owner's toll.
In recent years, some hitchhikers will go to some bulletin boards or websites to make an appointment in advance and contact some people who are willing to provide hitchhiking service.