The greatest sign the miracles of the stick and the hand. As explained in some other verses:
﴾فَأَلْقَى عَصَاهُ فَإِذَا هِيَ ثُعْبَانٌ مُّبِين % وَنَزَعَ يَدَهُ فَإِذَا هِيَ بَيْضَاء لِلنَّاظِرِين ﴿
(Then [Musa (Moses)] threw his stick and behold! it was a serpent, manifest! % And he drew out his hand, and behold! it was white (with radiance) for the beholders.) (Al-A’raaf : 107-108)
When Pharaoh gathered the sorcerers to challenge Musa (pbuh) at that time, Musa (pbuh) threw his stick, which then swallowed up the falsehoods.