indicator

/ˈɪn.dɪ.ˌkeɪ.tə(ɹ)/

ot noun

A pointer or index that indicates something.
A meter or gauge.
The needle or dial on such a meter.
Any of many substances, such as litmus, used to indicate the concentration of a substance, or the degree of a reaction.

Manbalar: Wiktionary (Free Dictionary API orqali), Datamuse, Tatoeba (CC BY 2.0 FR), MyMemory.