Yes, the cross is a remnant of a heinous crime -- the state-orchestrated murder of Jesus of Nazareth. But because Jesus was victorious over death, evil, and hell, the cross became a sign of life, hope, and God's power.
This cross in the ruins of the World Trade Center is just such a sign -- a remnant of a heinous crime, but it is nonetheless a sign from God, even if in your distress and anger you must reject it as such.
"How great are his signs! and how mighty are his wonders! his kingdom is an everlasting kingdom, and his dominion is from generation to generation."