That's the lvl 76 arcane artifact proc not the belt proc.
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Its belt proc, the 76 aa proc is same but you see a damage buff icon under your mana bar, for the belt you see two buff icon a defence one and another one that resembles rogue speed ultimate icon
It doesn't have a visual or an icon when procs. Tbh I think it doesn't proc at all. It needs dev revision or fix.
~LUCKYLOBO~