The most recognizable symptoms include having an earnest and idealistic eagerness to help the more marginalized members of a society, such as persons of color, or the homeless. This can manifest itself through things like bake sales and canned food drives, although occasionally, more touchstone examples (such as that of a teacher assuming the role of mentor and parent) can be observed.
Nice White Ladies (or, NWL's) know that they are just that, though believe wholeheartedly that not only do their contributions actually change the world significantly, but that they are somehow better than everyone else. There is more than a tinge of irony in this.
The male equivalent to Nice White Lady syndrome is the Savior Complex.
Terry: The nice white lady at the church gave them to me.
Aisha: That teacher ain't so bad.
Tameka: Only cause she got Nice White Lady Syndrome.