No, "Om" and the Christian cross are not equivalent symbols.
Om (also spelled Aum) is a sacred sound and a spiritual icon
in Hinduism. It signifies the essence of the ultimate reality,
consciousness, or Atman (soul). It is considered to be a symbol of the universe
and the underlying cosmic sound that sustains it. Om is used widely in Hindu religion and to a certain extend in Buddhism, Jainism, and Sikhism, but its significance may vary slightly across
these traditions.
On the other hand, the Christian cross is a symbol
representing the crucifixion of Jesus Christ and is central to Christianity. It
represents the sacrifice of Jesus for the salvation of humanity and is a symbol
of faith, redemption, and divine love for Christians. The cross is not directly
comparable to Om in terms of symbolism or meaning.
Om is more than a symbol it is cosmic and is focused on inner experience and consciousness. Om is more individual focused as it helps an individual realize that all animate and inanimate are connected to the primordial source.
Cross is more historical and is outward looking while Om is always inward looking.