So I had researched it a while ago and don’t recall having found anything effective and non-suspicious to protect from public camera mass survaillence in cities and the like. Is there anything that is a good option for that yet, and if so, could you point me toward it?
I’m thinking it’s a conflation with a basic “invisible ink” made with lemon juice.
You write a message in lemon juice on paper; the juice dries clear, then you can heat the paper to darken the juice and make the message legible.