SSDR, 4 people have told you how those rules works, and how it's always been used in play. I can't make you agree, and if I could I wouldn't. But you haven't responded to ether points concerning Gaes or the optional rules that do make it obvious. Sustained spell can be spotted by astral or by why was discussed by Kiir.
The Tactics rules are for when guards see people cast spells in front of them. Other magic are pretty obvious, most elemental indirects fireball, lightning bolt those sorts of spells. High force direct can be kinda obvious, gonna take a decent amount of force to drop someone with stunbolt, but then again someone walks in reagents a stunbolt, effective force of 1, odds anyone spots that is super low, that's all working as intended. But there nothing in there that says they spot quickened spells man. Try reading it from our interpretation and you can see it works just as well that way.
Well I'm participating in the thread because I do want to understand alternate points of view, so I appreciate your humoring me. My difficulty with what you've been saying is that it doesn't jive with what the rulebook says. Doesn't matter what you say the rule says, the rulebook says what it says. And it's been quoted repeatedly upthread so I won't quote it again here.
Near as I understand you, you're saying that either you can't notice any magic at all if it's not during the casting, or that sustained/quickened spells are not analagous to Wards for the purposes of this rule. Obviously you can notice magic post-casting, or else there wouldn't be a mechanic spelled out for doing so (6-F formula) and an example given doing so (noticing a Ward without mentioning the Ward's creator's Ritual Spellcasting skill level as being relevant). The rulebook also uses the language of "skills" as opposed to mentioning "spellcasting" specifically, so sustained spells can't be non-analagous to Wards on the basis of being different skill. The rule and example make an implicit but IMO clear statement that magic doing nothing other than passively existing is potentially perceptible on the physical plane, even by mundanes. I'm simply not following your logic when you say by implication that spells don't count.
As for my lack of answers to your points: Yeah I've ignored them, but that's because I don't understand what you're getting at rather than bad faith arguing. What about Geasa and optional rules render moot the rules as described in the core rulebook on pages 280-281? Honestly. Give me a citation and let me see what you're looking at, because I've played since 1st edition and I have what I consider to be a better than decent understanding of how the magic rules have changed over the editions and yet I still have no idea what you're talking about with regards to Geasa (they are voluntary restrictions on the performance of your magic as a means of making magic easier- it's been that way since the 1st ed Grimoire and confirmed for 5th in SG on pg 142).
Edit: If any Mods happen across the thread, it'd be super if you could split the thread out from
Sphinx's post and use the discussion since then as a new thread entitled "Can mundanes see Sustained Spells?" or such. Greatly appreciated.
Edit2: Thanks!