A final sign with many implications....
Mathematics includes other cautions...perhaps they should be included as labels:
Every zero should carry the label: Do not use as the divisor.
You probably can make up your own cautionary labels...I invite your student's creative responses. And, you might share these actual labels that are painfully humerous:
On children's cough medicine: Do not drive or operate machinery.
A Halloween Batman costume: This cape does not give the wearer the ability to fly.
A television owner's manual: Do not pour liquids into your television set.
A box of rat poison: Warning: Has been found to cause cancer in laboratory mice.
A camera: This camera only works when there is film inside.
A steam iron: Never iron clothes when they are being worn.
A baby stroller: Remove child before folding.
A microwave oven: Do not use for drying pets.
Again, I await your student's creative math warnings....for inclusion later on this web site.