necessarysign
nounUK /ˈnɛsəsəri saɪn/
US /ˈnɛsəˌsɛri saɪn/
A necessary sign is a sign that you must have.
The teacher said the name tag is a necessary sign for the school trip.
OTHER MEANINGS
2. A sign that shows something is needed.
The wet floor sign was a necessary sign to keep people safe.
3. A mark that must be present for something to work.
The doctor looked for a necessary sign of health on the chart.
4. A symbol that is required by rules.
Every car needs a necessary sign on the back to show it is registered.