The piston items will have a very noticeable shadow atop the top of the item in inventories and GUI's. This is very similar for these blocks (in item form): Piston, Sticky Piston, Beacon, End Portal Frame, Enchanting Table, Anvil

This is pretty noticeable, so this has most likely been reported before.
By the way thanks if this is seen! Love ya Mojang!

~TrickyPiston