Upvote:0
Bhante Analayo writes in detail about signless concentration in Compassion and Emptiness in Early Buddhist Meditation. According to him, signless concentration is when nothing is perceived, but perception exists. This is not neither-perception-nor-non-perception because state has reduced perception while the signless has regular perception. I have not experienced either of those states so I'm going from what I've heard from others and inference.
Chapter Six (VI) Empty of Self is where he talks about the signless concentration. I cannot explain it better than Bhante Analayo.
Where to download his books for free, legally. https://www.buddhistinquiry.org/resources/offerings-analayo/publications/
Upvote:2
Following audio explains the meditation on Cūḷasuññatasutta where animitta cetosamadhi (signless/themeless concentration) is explained at 45:40.
Once you reach seventh jhana concentration (plane of nothingness) and if you are successful in understanding the impermanence of perception, then you can reach signless immersion of the heart (aka liberation due to wisdom - no sign of permanence). When you understand the perception to be void of self, you can reach release of the heart through emptiness. And when you understand perception is suffering then you reach the desireless abiding.
In Cūḷasuññatasutta the Buddha explains even these liberations are constructed, impermanent and subjected to cessation.
‘Even this signless immersion of the heart is produced by choices and intentions.’ They understand: ‘But whatever is produced by choices and intentions is impermanent and liable to cessation.’ Knowing and seeing like this, their mind is freed from the defilements of sensuality, desire to be reborn, and ignorance. When they’re freed, they know they’re freed.
Therefore, Nibbana is where our aim should be. And for that, the practice or the development you need is the Noble Eight Fold Path.