All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are not obliged to resign from your job, but you are only forbidden to supervise that kind of jewelry and you are permitted to supervise other kinds of jewelry. Indeed, we have already issued Fatwa 88353 clarifying that it is forbidden to sell golden jewelry which takes the form of a cross. Therefore, you should endeavour to advise your Muslim director and clarify to him that producing those crosses is producing non-Muslim symbols and helping in spreading the non-Muslim rituals. If he accepts your advice, then this is what is required, otherwise, it is not permissible for you to supervise the jewelry that is produced in the shape of a cross.
Allaah Knows best.