Most stores nowadays use cameras ion their premises, and this is known to any reasonable person with knowledge of how things go in California, or even the U.S. or in the Western World. In California, one must be able to assert an objectively reasonable expectation of privacy. If one does not see the camera while it’s there, that would be a subjective reason for expecting privacy, and such would not rebut the commonly known fact that almost all stores record with at least one camera.
This may provide for most scenarios a plausible defense without putting out a camera recording notice, but certain facts may, in fact, rebut this expectation. (Say, a tourist from a country where this is not the case barely having had an opportunity to learn about these customs in California) But one can imagine this to be a difficult burden to overcome and establish an objectively reasonable expectation of privacy based on the objective facts of their own country. It is also hard to imagine one to convince the police or the DA to prosecute or an attorney to file suit in a civil case on such a matter.
However, if no harm in it, it is arguably even stronger of a position to have that sign on the wall.
The fact that a video camera does not record audio may be a moot point; communication may transverse through body language, and even silence can be communicative; in fact, a case on confidential electronic communications provides decided by the California Supreme Court provides the following:
“[B]ecause it is beyond question that sections 632 and 637.2 [of the California Penal Code] are primarily intended to protect the privacy of the communications of California residents, we conclude these statutes must be interpreted broadly to apply to all recordings of such communications—whether one-sided or two-sided[; a]ny contrary interpretation would permit a business to maintain a policy and practice of recording one side of every telephone conversation with its clients without first obtaining the consent of all parties—a significant reduction in the scope of CIPA.” (Gruber v. Yelp Inc., 55 Cal.App.5th 591, 269 Cal. Rptr. 3d 790 (Cal. Ct. App. 2020)) (bold type added)
This shows that merely recording the fact that information was conveyed to someone without their knowledge may constitute a violation, and it is hard see why that would differ, for example in the case of an armed robbery where pointing the weapon is arguably very communicative and persuasive at that.
For one wanting to use such a recording and not having to establish that it is common knowledge that stores record etc. it appears more reasonable to proactively give conspicuous notice of the recordings so that a recording may be offered into evidence with less hurdles.