What does the Trained in a trap stat block mean?

[shade2077]

Some traps list a Stealth DC in their stat block and some list Stealth DC (Trained). What's the difference? Seems to be the 'Trained' is where the trap would list the level of training in Perception to spot the trap. All character classes are currently either Trained or Expert in Perception so there is no effective difference between a 'Trained' trap and one without a 'Trained' tag. So is the 'Trained' there in case classes (or companions) are introduced that are not Trained in Perception? Or perhaps some traps need 'Expert' in Perception to spot, rather than just 'Trained'?

Puzzled.

[Dante Doom]

A untrained can be spotted even if nobody is looking for it.
A trained Hazard can only be found for someone that have this profiency and is actively seeking it.