This is a phrase that I've seen in basically every spell that creates something temporarily, or temporarily changes the form of something (e.g. the Precious Metals focus spell).
I understand the rationale behind it (even though I disagree with it - players should absolutely be able to scam NPCs, with all the negative and positive consequences that entails), but that's beside the point.
How can people tell that the effect is magical and temporary, especially the latter? Sure, maybe the item is surrounded by swirling magical energies, making it obvious that magic is at play somehow. But what about the effect makes it obvious to Joe Barbarian, who has never seen a spell like this in his life, that the effect is temporary?
This isn't explained anywhere, and I can't really see any way to justify it short of every such affected item emitting a holographic image of "this item reverts to it's natural form in:" and a countdown, or some similar effect. Either that, or every single citizen of every single culture, regardless of how remote, has been so intensely educated from birth in identifying every spell that could be used for fraud, that they can instantly identify such effects without an Identify check.
If this required a Perception or Arcana/Religion/etc check against spell DC, it would make sense, but the fact that any person can immediately identify the effect as temporary with a casual glance is difficult to justify.
It crackles, Sparks slightly, some of the bits that are supposed to touch don't, glows faintly, smells like purple, things like that.