Board Thread:Episode Discussion/@comment-26397825-20171028154114/@comment-201.141.215.86-20171030040950

The emblem only appeared after the glove with the Grimm fused with her skin so I'm more inclined to think it's a result of the Grimm living inside her rather than the Maiden's power. We see her eye shine with the power but it's only after she absorbs the Bug Grimm that the tattoo appears.