I'm not taking WYSIWYG to an extreme. I'm just saying that it isn't really a good shield to hide behind (get it? shield?) when you consider all of the other limitations of the NWN engine and VFX on the module which, if they followed the same set of rules, would also be absolutely WYSIWYG. A rule is not a good rule if it has to have asterisks placed after it for every incident, though then again perhaps that is why this rule is an unspoken one and not actually listed in the player journals or forum rules compendium.
For the record, under that same argument: Divine magic isn't scripted to provide any clues to differentiate between itself, and Arcane. Sorcerers and Wizards aren't, except for the OCR system (Perhaps that should be the new rule? Cast infront of the NPCs so they can tell me if you're a Sorcerer or not?)
Each Shield does have a unique set of modifiers. If you're Lawful Good, if you hit someone, they'll have DR; If they're Evil, they won't. These things can still be deduced to a certain extent and 'tested' through in-game mechanics, but those are awfully clunky ways of doing so. There are also weapons and tools you can use on people to deduce their alignment, I suppose if that was really your aim. After-all, Bards have a Dirge of Woe which effect Evil, Neutral, and Good wholly differently and presumably could deduce via how it effected them, where they sit on the alignment scale.
If each of these Shields is unique, then it's unique. Religion was never a huge area for ambiguity in Dungeons & Dragons, anyways. Maybe other players can't, at a visual glance, learn what the Shields are, but I imagine someone at your Sect will. If you were an Acolyte of the Third Revelation in Dementlieu taking their trials, and you manifested your shield before Bastion Caille (Formerly, Seccousse)\, surely they have an inkling or are aware of the signs of a new Sect, or their own. Meaning it wouldn't make sense for someone within the Third Sect to have been brought into the Third Sect but secretly hiding their Lawful Goodness, Lawful Evilness, or so forth. I imagine if your alignment shifted whilst within a particular Sect, you aren't manifesting your shield all the time anyways, but you'll probably more sooner decide to shift to a Sect that you can morally agree with.
I think we'd have to have some manner of clarification as to how these Shields are unique from the DM Team, because one way or another, they are, and they've been roleplayed as such in-character for the last decade or more. If you remember Inquisitor Martel, he was all over the alignment axis, and served in a Sect that did not match his own alignment. However, he hid his Shield, and as an Inquisitor, who's going to ask?