Here are the fruits of my Victorian frailty. I took Kate's advice and made a sampler - not of a slogan, admittedly, but still something I can believe in. It made a very nice pair of afternoons - I sat out on my porch in the sunshine and our nice cool, 27C weather and had a pretend Victorian convalescence.
The sampler shows a formal way of writing a kind of logical operation known as modus tollens, followed by its proof by truth table. The embroidery is not quite finished; I'm going to sew in 'modus tollens' at the bottom but I made too many mistakes trying to write it out with the erasable fabric pen so I had to wash the fabric and let it dry before I could try again, but you get the main idea.
The little sideways horseshoe indicates a conditional statement and means 'if...then'. The tilda means 'not'. The three dots in the form of a triangle mean 'therefore'. So the top part reads '1. If P then Q; 2. not Q; therefore not P'. Then the truth table lines up all the possible truth values for the whole thing. In non-modal logic, statements can be only true or false but not both and not undertermined. Anyhow, it shows that a conditional is false when the antecedent (in this case P) is true and the consequent (in this case Q) is false.
So now I have my own embroidered version of a fundamental logical truth about the world. That makes me happy. I plan to make one for modus ponens next. Thanks, Kate, for the suggestion!