[Sorcery] Are buffs obvious to the subject?

[Crystalline_Entity]

According to GURPS Thaumatology: Sorcery, buffs have "No Signature" so they're not obvious - I'm assuming that this means that there's no evidence to a third party that a spell was just cast. However, I was wondering whether it was obvious to caster and subject when a buff effect was wearing off?

I'm assuming the sorcerer wouldn't - once the affliction has been cast, the spell is out of his personal control; he needs Cancel or Dispel Magic to end the spell prematurely, so I guess he also needs Detect Magic to know whether the buff is still active? I might be wrong, of course.

Would the subject be aware that the time was almost up though? For an obvious effect like flight I can imagine the subject descending gradually to the ground, but for less noticeable effects like Resist Acid would the subject be aware that the duration was almost up? Or is it a case of not realising that the acid resistance has worn off until you notice it burning you? If it's the latter, I think a good stopwatch might be come a useful bit of equipment!