In the Gandhara sculptures, the preaching mudra associated with the Buddha`s First Sermon at Sarnath is typically depicted as the Dharmachakra mudra. The Dharmachakra mudra is commonly referred to as the "Turning the Wheel of Dharma" gesture.

In this mudra, the Buddha is shown holding his right hand up, with the thumb and index finger forming a circle or wheel, while the other fingers are extended. This gesture symbolizes the Buddha`s teaching and the turning of the wheel of Dharma, representing the dissemination of his teachings to his disciples and the world.

The mudra signifies the Buddha`s first sermon at Sarnath, where he preached the Four Noble Truths and expounded the Eightfold Path, establishing the foundation of Buddhism. The Gandhara sculptures, characterized by their Greco-Buddhist artistic style, often depicted the Buddha in various mudras, including the Dharmachakra mudra, to convey important aspects of his teachings and significant events in his life.