Why "Crossing our T's?

I decided to keep a blog about the journey we are taking to adopt a little girl - possibly from Taiwan. Most of the girls names we like either start with a T or have a T in them. We were trying to think of an expression as a theme for our blog and we decided since we have an Isabella and the adoption of this little T girl is partly to give her a little sister, we've already dotted our I - now we are crossing our T! This little girl will COMPLETE our family! This will be our Princess "T".