User blog comment:Sorairo/Aura, Dust, and the RWBY Panel/@comment-11188061-20130823055451/@comment-11188061-20130823060528

Obviously not many people share the same... special feature. Since Aura is the strength of your soul (or something like that), and a soul is supposed to be unique. It's just like Ruby's special trait is her rose red petals. Thus Ozpin and Glynda obviously would not show the same thing when they used their Auras (which Glynda did not I presume, there are some visible (but possibly two way) proof that she was using Dust at that time).

However, for Crimson and Yang, both of them share a similar trait - changes in eye color. Perhaps Yang was interested because of it.

Though all of this seriously are just empty guesses. We first must have proof that Yang indeed knows Crimson before we can even begin to speculate.