Common practice is an inverting face-up the cards in discard pile and placing face-up cards discarded face-up on top of the pile, when effects like Hero Pallando comes in play (and when first card of opponent is being discarded).The Wizards: Pallando
Unique. His controlling player may keep one more card than normal in his hand. Opponent must discard his cards face up. "They came therefore in the shape of Men, though they were never young and aged only slowly..."-LotR Home Site: Grey Havens
I doubt whether it is a correct practice.
Firstly, it reveals more information that it is required. Player may search for a card in his face-up discard pile and then his opponent knows whether he chose top card or other card from discard pile. This is more information than just knowing an obverse of discarded card.
Secondly, the situation complicates in multiplayer games. Not only the players allowed to see an obverse of discarded card have above information, but all players have access to them.
"avers" -> "obverse"