The "clear signs" mentioned in the verse refers to the miracles which- had manifested themselves even before the Torah was given to Sayyidna Musa (Moses علیہ السلام) -- for example, his staff that turned into a .snake, the palm of his hand which shone brightly, the splitting of the sea to make a path for the Israelites, etc. These miracles were meant to affirm the Oneness of Allah and His omnipotence, and to provide an evidence for the prophethood of Sayyidna Musa۔ (علیہ السلام)
In refutation of the Jews, the verse points out that although they lay a claim to 'Iman ایمان (faith), yet have been falling into the sin of Shirk شرک (association), which involves a denial not only of Sayyidna Musa (علیہ السلام) but even of Allah Himself.
Although the Jews who were the contemporaries of the Holy Prophet ﷺ ، did not themselves take part in the worship of the golden calf, yet they respected such of their forefathers as had done so, and took their side. So, for all practical purposes, they too were guilty of the same sin.
The verse also suggests that no wonder if these people, whose forefathers denied Sayyidna Musa (علیہ السلام) ، should now be denying the Holy Prophet ﷺ .