Can a public entity or public employee be held liable for failing to post a warning sign?

Section 830.8 does have a caveat: "Nothing in this section exonerates a public entity or public employee from liability for injury proximately caused by such failure if a signal, sign, marking or device (other than one described in [s]ection 830.4) was necessary to warn of a dangerous condition which endangered the safe movement of traffic and which would not be reasonably apparent to, and would not have been anticipated by, a person exercising due care." To fall within this exception there must be a failure of a traffic control device that was designed to warn of an otherwise dangerous condition. (See Pfeifer v. County of San Joaquin (1967) 67 Cal.2d 177, 184 [exceptions to section 830.8 "do not come into play until existence of a 'dangerous condition' within the statutory definition is first shown"]; Mixon, supra, 207 Cal.App.4th at p. 136 [dangerous condition "may require the posting of a warning sign but the absence of a warning sign itself is not a dangerous condition"].)