To record a video on your phone you need to hold your phone up pointed at the other person, usually not in the same way you would normally use a phone. If you see someone holding his phone steady at face level and pointing at something without making finger movements, you know he is filming. If someone is pointing his phone down towards the ground and scrolling around with his thumb, you know he is probably not.
To record from a pair of smart glasses you just need to look at someone, as you would normally look at any other thing. Yes there will be an LED on, but the person being recorded probably couldn't see it if it is in a bright, busy environment and you are more than a few steps away, plus there will be aftermarket modifications to disable the LED. In short, there is no way you can reliably tell if someone's smart glasses are filming you. You have to assume that worst.
Then again, there may be some selection bias at play…
https://www.nytimes.com/2025/11/21/nyregion/nyc-nightlife-no...
You can keep your phone here but the cameras are taped off. Of course that can easily be undone but it avoids the "oh sorry I forgot it wasn't allowed" excuse.
The world is not deterministic, and we can shape norms of how we interact with each other. We don't have to accept being constantly recorded just because the technology makes it possible.