If I remember correctly, the JWs in their Babylon the Great book, made the following arguments.
1. The cross was derived from the pagan Egyptian symbol known as Crux Ankh which looked like this
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This cross was supposed to be a phallic symbol incorporating the genitalia of male and female. As you can tell by the image that argument is stretching it quite a bit.
2. Then there was the argument that compared the Christian cross with the Babylonian Tammuz cross which actually looked like a cross.
The counter argument is that the t shape is so simple that someone is bound to use it even if there is no connection with each other. A child doodling with a pencil or a chimpanzee with a paintbrush could draw a t .
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