It's possible that we'll learn similar patterns for Glass. While we won't know if the device itself is recording, we might still be able to guess based on where the wearer is looking and how quickly they are moving. On the flip side, Glass wearers might also change their postures and habits so as to avoid matching these newly-learned patterns.
Don't get me wrong, I do think its unfortunate, because there are real positive sides to the device, and you touch on them in your blog, but for me, unless I feel better about the hair raising on the back of my neck, I'm going to be hesitant to accept the devices. (Caveat: I'm a bit of a privacy nut, that has never used Facebook, twitter, uses brivate browsing whereever possible, uses SMIME to encrypt most of my emails, etc., so my experience may not be very indicative)
In other words, it could be a lack of obvious physical gestures that indicates we are not recording, rather than the presence of obvious physical gestures that indicate we are recording.
A world in which we don't 'point' our heads at strangers is definitely weird and possibly undesirable, but interesting to think about.