I joined MN in 2013, whilst duffers with DS1. There was a lot of talk about a 'Mumsnet scarf' that you could tell if someone was a MN-er if they were wearing one - sort of leopard-print, maybe blue?
I asked one friendly-looking mum at a baby group once if her scarf was a Mumsnet scarf and she looked confused and mildly offended. Yay! Go me.
Other than that I never saw one, and actually it might have been a wind-up or in-joke I didn't get because I was too new and stupid.
But we should have a Thing. A subtle way of slyly signalling that we are Mumsnetters, right? But what could it be? 🤨