The silent rhetoric, or rhetoric tacens of art, may include commonly
encountered rheorical symbols, but symbols may be "silent"!
In this painting by Rembrandt, the preacher Jan Cornelis Sylvius is seen
very persuasively, literally reaching out of the painting. This is another
example of an Alberti "witness".
It was very common to symbolize "rhetoric" with the open hand. Preachers
commonly used rhetoric in their sermons. "Science" (logic) was viewed as
being in opposition to rhetoric, and logic was commonly symbolized with
the clenched fist. The intentions of Rembrandt are quite eloquent, but
"silent"!
Note: Jan Cornelius Sylvius married Alida van Uylenburgh, the cousin of
Rembrandt's wife Saskia van Uylenburgh.