In what circumstances can a jury infer that a witness has been shackled?

In People v. Valenzuela (1984) 151 Cal.App.3d 180, the court identified two inferences relating to the witness's credibility that the jury could draw from the witness being shackled. First, knowledge that a witness was incarcerated might permit an inference of diminished credibility. (Id. at p. 194.) Second, "the presence of shackles permits the inference that the witness is dangerous and has probably engaged in violent conduct in the past." (Id. at pp. 194-195.)