When my daughter asked me and my husband about a No Smoking sign, we explained that it means no cigarettes are allowed. (We had to explain cigarettes to her too.)
Unfortunately, she now thinks that the red circle and diagonal line are called a "cigarette", so she'll talk about the cigarette in the No Parking sign:
Is there a name we can teach her for the red circle and slash?
\x{1F6B8}\x{20e0}
or\N{CHILDREN CROSSING}\N{COMBINING ENCLOSING CIRCLE BACKSLASH}
. Note that it is a backslash, not a slash.