This is wild to me, as my rule of thumb is the exact opposite! I assume anybody whose profile picture isn't themselves is either a bot, a troll, or a throwaway account they use for comments they know will be controversial. It's the equivalent of having a username like "@John448172312". (Not that you should really trust either group to argue anything in good faith on Twitter).

There's a lot of nuance, but my rule of thumb isn't so far off from the comment's above you.

My Twitter avatar is a picture of a fractal I generated with my own software. That reveals (fuzzily) a certain non-obvious aspect of my personality, which you couldn't get just from looking at my face. The majority of people have faces; mine isn't much of a signal to strangers.

Faces are for recognition. If we met at a conference, you could recognize me again by my face. If you don't know me, my face isn't very useful unless you expect to meet me in person. So, a face on Twitter is unhelpful to the point of being counterproductive.

Anyway, that face might not even be theirs.

That's an unfortunate heuristic. What is your basis for this?

Unwarranted self-importance. Bonus points if it's a photo of them on a stage holding a microphone with that open-palm I-am-giving-a-TED-talk gesture :)

I know someone who hates pictures of herself, never took a selfie in her life, but switched to a picture of herself and used her real name simply because it's less likely she'll say something stupid/inflammatory in the middle of an argument. If you're using some random name like chickenslippers1981 and have a pic of a cat, you might feel less like being thoughtful. You can always walk away from chickenslippers1981/cat, but you can't walk away from yourself.

This is probably a pretty decent heuristic actually! My guess, as an armchair psychologist, is that narcissism and a toxic need to generate attention and drama are highly correlated with constantly taking selfies and sharing them. Look for the profile picture and just a quick glance at the feed, and if it's full of selfies, you probably have a pretty good idea of who you're dealing with.

As another armchair psychologist with an ex-girlfriend that was just like that, I can confirm.

I fall in to that group so you're probably right not to.