I imagine structions are rated on a danger-scale from A through D. An A is precautionary for ‘in the unlikely event’, but be aware something can go wrong. A B denotes a strong likelihood of minor injury or inconvenience. C, you can really get hurt. D, there’s no hope at all. O? Well, that’s a blood type. If you have an O “B” Struction, there is a risk of clotting.
Grrrrooooooaaaannnnn!! Well, in the words of a beloved friend, “I crack me up!”
Have a wonderful day!
p.s. The photo was taken from a Narrow Boat on a canal in the the UK.