(1) the frames are asymmetrical, partly dismantled or completely absent;
(2) content may come in the form of abstract non-representational shapes which might be arranged within panel borders or illegible writing may be placed in speech balloons, and
(3) comics conventions (no not the ComicCon or Supanova kind!) such as speech or thought balloons which may be used within a different artform such as visual art or poetry.
(This brings to mind that an old uni friend recently told me through FaceBook that his PhD was a combination of poetry and comics ... he's sending me a copy so it will be interesting to see if it fits Tim's definition of abstract comics.