Exercise 1: Affordance vs. Signifier — Possible Solution
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Affordance and signifier are not interchangeable in Norman's own real
usage - he introduced signifier specifically to separate two things
his earlier, narrowed definition of affordance had blurred together.

A perceived affordance is the actual possibility of an action - a
clickable element is genuinely clickable whether or not that fact is
visible to a user. A signifier is the visual cue that communicates
that possibility to the user - a drop shadow, an underline, a change
in cursor. Norman himself later acknowledged that narrowing
"affordance" down to only the perceivable version had blurred this
distinction, which is exactly why he introduced "signifier" as a
separate term: an element can technically afford an action (Gibson's
original, broader sense) while having no signifier at all, meaning
most users will simply never discover that the action is possible.

ANSWER: This is inaccurate - Norman introduced "signifier" precisely
because he found his own earlier use of "affordance" had blurred two
different things together. An affordance is the real possibility of an
action; a signifier is the visual cue that actually communicates that
possibility to a user. An element can afford an action without any
signifier present, and in that case most users won't discover it.

WHY THIS WORKS AS AN ANSWER
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This correctly reproduces the chapter's own real distinction and cites
Norman's own honest self-correction as the reason the two terms exist
separately, rather than treating them as synonyms.