Yeah, poorly written.
Yep, a 2/2/2/etc build would do.
On attaining 2nd level in any class, an illumian gains
a second different power sigil, and the bonus granted
by each power sigil increases to +2. Depending on the
combination of power sigils she chooses, an illumian
gains one or more extra special abilities (see Illumian
Words, below).
By a strict reading, they only get 1 extra sigil; however, by a looser reading, they do get one every 2 levels. RAI seems to be that they only get two, so...
"On attaining 2nd level in any class ... "
If that 1st sentence could be split and isolated, I think the case would be stronger.
But since it continues
" ... an illumian gains a
second different power sigil, and the bonus granted by each power sigil increases to +
2."
Seems kinda nice for T.O. but otherwise r.a.i. is obvious to stop at 2.
WOW, gotta have those +1 LA Illumians please !!