Umbrella, WFL may turn out to be her biggest selling single worldwide in the long-run but Umbrella remains to be the single that changed her whole career and public perception of her and made her into the worldwide star she is today and is her most critically acclaimed single and one of the best songs of the 00's decade so Umbrella.
Umbrella because that really showcased her vocal ability and that's a song only rihanna could pull off and no one else
I tend to think an artist signature/iconic song is one that both shows off their vocal ability and one that only they could pull off...nothing could even come close to the original
