Huifeng wrote:These are a couple of, but not all of, the interpretations of the signless.
Well, that's actually even more interesting.
The earliest formulations have emptiness (sunyata), signless (animitta) and nothingness (akimcanya)!
But, even some fairly early sutras of the various schools started using intentionless (apranihita) instead of nothingness.
One can easily track them through a range of early sutras, into the various early sectarian sastras.
And, while some schools went emptiness, signless and intentionless, other swapped the order of the last two, emptiness, intentionless and signless.
However, the basic interpretation of intentionless was to have no inclination towards any phenomena, again a subjective stance.
Slightly later, it was considered that this state of absence of intentionality was a characteristic of phenomena themselves, or rather, that the lacked the characteristic of intentionality.
A lot of subjective stance move to objective stances, mainly under the influence of Abhidharma and competition from other systems in India towards ontology and metaphysics. At least, that's my take on it.
It is also fairly common to link the three by indicating that whatever is empty is devoid of signs, and therefore one cannot have intentions towards signless phenomena.