See which pokemon has an item once frisk has been triggered similar to when yours has one.

[Octopice]

Quite literally just the item indicator on the wild pokemon that has an item once frisk is triggered, simple but really helpful

[ChihuahuanRaven]

This used to be a feature, but has since been removed for balancing. I have doubts they'll bring it back since it was only available for a short time.

[SacredDiver]

I believe that the mechanic used to be "You can see which Pokémon has an item but you have to avoid KO'ing it in order to thief the item successfully", you can't see it anymore now but you get the item even if you KO the mon. The feature was intentionally removed for balancing reasons like the comment above me says.