The ancient symbol of the Trinity, representing The Father, The Son and The Holy Spirit, as THREE in ONE.
For as long as I can remember, when I sit and doodle, I've always doodled triangles, coming out of triangles, coming out of triangles. Once, I covered the entire front cover of the phone book with them. It was very cool. Although, if memory serves, "cool" was not what my mom said when she saw it.
So naturally, the first time I ever saw the symbol for the Trinity, I thought 'hey, now THAT is cool'. Now, instead of phone book covers, I get to doodle on t-shirts.