The cross was definitely not a holy image in pre-Christian Judaism.

Crucifixion actually had heavy stigmas attached to it by both Romans and Jews. For the Romans, it was typically reserved for low-class criminals like thieves, rebels, or pirates. In Roman society, Jesus' crucifixion would have marked him as a particularly ignominious character, hardly to be worshiped or even admired. The earliest depiction of Christ on the cross actually comes from a bit of second-century Roman graffiti mocking the idea of a crucified God: the Alexamenos graffito. It's a bit hard to make out, but the image depicts a man bowing down to a crucified figure with a donkey head. The caption reads: "Alexamenos worships God" - a snide remark at Christians, no doubt.

Although crucifixion was not a traditional Jewish form of execution, stigmas against death by hanging seem to have carried over. Deuteronomy 21:22-23 actually posed a challenge to early Jewish Christians. "If someone guilty of a capital offense is put to death and their body is exposed on a pole, you must not leave the body hanging on the pole overnight. Be sure to bury it that same day, because anyone who is hung on a pole is under God’s curse." The implication, of course, is that a crucified person ("hung on a pole," in a manner of speaking) must be cursed by God. You can see the early Christian response to this problem, for instance, in Paul's writings (Galatians 3:13): "Christ redeemed us from the curse of the law by becoming a curse for us, for it is written: 'Cursed is everyone who is hung on a pole.'"

The cross only became a holy symbol by association with the worship of Jesus, and with the significance of the crucifixion in Christianity. Before, during, and immediately after Jesus' death, the cross was merely a particularly stigmatized form of death.