DAY 431

Give me an X, I'll turn to face you.
Give me a cross, I'll turn my back on you.

OR

Give me a cross, I'll turn to face you.
Give me an X, I'll turn my back on you.

Who am I?

Answer:

The number 9:

9 x 9 = 81
9 + 9 = 18

OR

9 + 9 =18
9 x 9 = 81