A lens with a cap on it settles the question
Raven Prism, an early-stage device previewed at AWE this year, includes local inference and a physical cover over the camera. Tony Vitillo wrote up his impressions of the glasses and their privacy approach, and it is worth reading as an example of the design direction rather than as a product recommendation, since the thing has not shipped.
The cover is the part we keep coming back to. Everything else in a privacy specification lives inside the device, where the only access a stranger has is a claim printed on a website. A piece of material sitting over a lens is different in kind. It is visible, it is unambiguous, and it cannot be quietly reversed by an update pushed overnight.
Legibility outranks strength
A determined wearer defeats a cover in one second by sliding it open, which makes it a weak control by security standards. That is the wrong measure. The point of a cover is not to stop somebody who intends to record. The point is that it makes the ordinary case readable, so a person nearby can tell the difference between a device that is off and a device that is watching without having to interpret anybody's intentions.
That is a lower bar than the industry has been aiming at, and a more useful one. We would rather have a weak control that a stranger can read than a strong one they have to believe in.
The convention does not exist yet
Physical covers only work if the closed position is the default and if it looks closed to someone who has never seen that model. Right now every manufacturer that ships one will design it differently, and a bystander will be asked to learn a new vocabulary per product.
That is the kind of thing a standards body settles early or never. Nobody has taken it up. Meanwhile the feature sits in a boutique device at enthusiast pricing, treated as a differentiator for buyers who care, when it is the only part of the arrangement the people outside the purchase can actually use.