In the Gandhara sculptures the preaching mudra associated with the Buddha’s First Sermon at Sarnath is

The preaching gesture associated with the Buddha’s First Sermon is the dharmachakra (wheel-turning) mudra. Art-historical treatments state that the wheel (dharmachakra) stands for the Buddha’s first sermon at Sarnath, and sculptors used gestures that represented this event rather than literal narrative props [1]. Iconographic and museum descriptions of Sarnath imagery explicitly identify the teaching posture as the dharmachakra pravartana mudra — the gesture of “turning the wheel of Dharma” — used to depict the Buddha delivering his first teaching, a motif also referenced in Gandharan and related sculptural traditions [2]. Thus the correct option is dharmachakra.

Sources

1. [1] THEMES IN INDIAN HISTORY PART I, History CLASS XII (NCERT 2025 ed.) > Chapter 4: Thinkers, Beliefs and Buildings > 9.2 Symbols of worship > p. 100
2. [2] https://en.wikipedia.org/wiki/Buddha_Preaching_his_First_Sermon_(Sarnath)