The domain of f(x) = x^2 sgn(x) is all real numbers.
The function is defined for all values of x because x^2 is defined for all real numbers, and sgn(x) is also defined for all real numbers except for x = 0. However, when x = 0, the value of f(x) is also defined as 0.
Therefore, the correct answer is A) All real numbers.