A long while back, there was a bug in World vs. World in which a mesmer could easily be separated from their clones visually because the mesmer him/herself displayed the world completion icon, while the clones did not.
For world vs. world, this was fixed.
This bug has resurfaced in the Guild Hall Arenas. Mesmer clones are easily distinguishable from the primary because world completion icons/etc. are absent from clones.
Where are my gem sales? I want gem sales! Nerf EVERYTHING!