I think there are some obvious signs that you are in the presence of a blogger:
They're always taking photos - in the supermarket, out for a walk, cooking a meal, eating a meal - they're always clicking away because they never know when it might come in handy.
They get twitchy if they have no internet access.
They say things like "I can feel a Silent Sunday coming on" and "I can relax now that I've done my Gallery post."
When taking photos of their children they will say things like "C'mon, you know you're not supposed to look at the camera!" I've witnessed this myself, haven't I Rosie Scribble?
There will be a pile of items, waiting to be reviewed, stacked up somewhere in their house.
They have an area of hard skin just above their knees where they balance their laptop.
They have perfected the art of blogging and watching TV at the same time, and everybody knows what they're watching because they tweet about it.
They're constantly checking their phones for emails, tweets, facebook updates. God forbid they should leave their phone at home and have no way of checking how popular they are.
Every unusual, happy, interesting event is blog fodder, and if writing it in retrospect they may even stage re-enactments and take photos. Believe me, it happens.
Their children say things like "you're obsessed with your blog!" or "take a photo for your blog Mum".
When a group of bloggers meet they spend most of the time tapping away at their phones.
They're the tell-tale signs I can think of, can you think of any others?