You do not need a trigger.
Simply make the item display the model, it can not be simpler. This has been seen by items such as the banners.
Yeah, for example, base it off of Orb of Fire, or if you don't want to, some ability(modified) like Endurance, Brilliance, Command, Devotional, etc and just remove the effect.
Remove the effect(like the +damage bonus if you don't want that), change the "Art - Target" to the model you want.
Change the "Art Attachment Point 1" to "weapon" or "weapon" "left" if you want it to appear on the left hand side, or "weapon" "right" if you want it to appear on the right hand side.