Board Thread:General Discussion/@comment-7242608-20140604015723/@comment-4010415-20140617205540

Callie Heart wrote: Sure the tatto seems like her insignia and it may well be, but we don't know quite what it does exactly. She doesn't exaclty have any weapon to channel her fire and the tattoo didn't light up as the designs on her dress did.

I'm going to wait and see if the tatto really is her insignia. I have a feeling we might find out in Volume. 2 It's an insignia, not a power source. It's an emblem. A symbol. A family crest. Whatever you wanna call it. Each character has one. Ruby has her scatter rose, Yang has her flaming heart, Blake has her nightshade flower, Weiss has her snowflake, Jaune has his rainbow, etc and so forth.

As for what Darkcloud said, here's an image.