And for the evil overlord you want to put the Sigils into Symbols, Spell Triggers or Wards.
I don't think you can, since Sigils are explicitely not "spells" in themselves but rather equivalent to rune spells "that automatically 'enrunes' a specific spell". As such, putting the Sigil into a Ward (for instance) would
cast the Sigil when the
Ward activates rather than activate the Sigil ("read the rune"), resulting in the Sigil's spell equivalent to be 'enruned' rather than to be cast. In other words, casting a Sigil spell doesn't produce its effect but 'enrunes' its effect as a rune onto a rune paper. One then have to explicitly reads the rune…
BUT these can be seen ahead of time and shut down (my groups gotten good at that).
See? Through walls? A Runemaster's Ward covers an area of 10'R/lvl (just the same as the Sigil of Pain's effect, so it's really absolutely perfect!) Considering that most spells (including detection and especially dispel spells) have a range of 100' or area of effect of 100'R (except if you're playing at very high level…), it means that at level 11 (which is not really high…), a Runemaster may cast a Ward that may activates before it is detected; if put "inside" the Tower of Evil™ —meaning there are walls between it and the "outside"— it cannot be seen either. Since it is "triggered by an event of the caster's choosing (e.g., time period, certain movement, certain sounds, touch, etc.)", the caster may just have it triggered when "intruders" (for instance any creature
not performing a certain sign, or speaking a certain password, etc.) enter its area of effect and, say, merely ring a bell (why? because an Alarm Ward is a mere level
2 spell!) When it happens, all the Runemaster has to do and take out his book whose pages are all an 'enruned' Sigil of Pain… and read one each round. Why a book? Because a book may be small and yet have, you know, hundreds of pages! Sure,
any, say three hundred-pages book where each page is a Rune is dangerous but a Runemaster may have
charged runes or sigil!!!
Remember that by level 12
only, he may give
each Sigil of Pain up to 30 charges! …so his book is the equivalent of three hundreds Rods without the encumbrance nor the spell limitation (a Rod may only have up to level 5 spells, and none even approaches the power of a Sigil of Pain!!)
Yes, producing such a book may take him some time but… The reason why the first
country that gains the magic knowledge to have Runemaster would dominate the world: because it may
mass-produced such books. Even if there are few actual Runemasters, all they need to do is to spend their days producing the pages of the book, with countless people channelling them the needed PPs to cast as many spells as possible (when creating a Rune Paper and enrunning it takes a long time, nothing prevents a Runemaster to create several Rune Papers
at the same time since casting a spell takes about three rounds / 30 seconds). Our world superpowers are defined by their nuclear arsenal; in a fantasy world where the Runemaster exists, that a country has the knowledge to form them and how many it has of them defines its position as a superpowers.
…including the potential Cold War state since the potential of destruction of actually using all these BMDs (Books of Massive Destructions) is… huge, especially when employed in inhabited areas, as such spells would kill people across the walls, grounds and ceilings of their houses!!
Imagine terrorists with such enruned Sigils of Pain~ It's just pages, so it's so easy to hide~
So, yeah, as I think I wrote, if you consider all the ramifications, merely having Runemasters in your world would change its face~
P.S. Yet, with all I said about the Sigil of Pain (remember that it's especially it that makes Runemasters so broken: sure, having a rune book with hundreds of thirty-charged fireballs is dangerous but a Fireball being a level 8 spell, one needs to be at least level 16 to cast the Rune spell, at least level 20 to embed it as a chargeable spell —reminder: a Sigil of Pain is the equivalent of a level 3 or 4 spell— and a fireball only has a radius of 10'R, being blocked by obstacles such as walls), I consider it merely the
second most broken spell of RM2/RMC (since an
even more broken spell was introduced in the CC!!!
)
