If you present me with a blue rectangle on a black screen, it's still confusing and cognitively-loading what the hell it's for or if it does anything. There are no affordances, only questions.
If you present me with a blue rectangle with an outset, stippled border on a black screen, it's clearly a button. Without that border that meshes with familiar previous training, there's no way to know it was a button. That's an affordance.
If a highlight or animation were added to the blue rectangle that already had an affordance, that would be a signifier.
Affordances are major indicators of action potential while signifiers are minor, helpful reinforcers of affordances.
The messy, subjective discussion is: what happens when all signifiers are thrown away, and then affordances too? Baby/bathwater defenestration.
https://ux.stackexchange.com/questions/94265/whats-the-diffe...