The title and Pastor Markle's discussion focuses greatly on the "verb" signified. So I looked it up and the word "signified" is actually a noun, while the words "signify" and 'signifying' are verbs. The definition of "signified" is "the meaning expressed by a sign rather than the physical form it is expressed in" (Collins dictionary). As a noun the word "signified" combined with "it" (signified it) can describe a state or quality, that is the state of revelations being in signs or sketches rather than literal.
A major problem with accepting that there is a mix is that people get to cherry pick which parts they consider literal and soon enough another revelation is born, a literal thousand years on earth after the resurrection is a long running beauty for example. No Apostle mentioned this and it's nowhere else in the Bible, and Jesus refutes it in John 18:36 (also Romans 14:17 is worth looking up).