telltale
n.a sign or piece of evidence that shows something is true or that something has happened. It is a clue that you can see or hear.
n.a sign, symptom, or piece of evidence that indicates the presence of a specific condition or event. Often used in technical or forensic contexts to describe a physical or behavioral indicator.
“The telltale signs of a leak are visible on the floor.”
“The telltale crack in the engine suggests that the part is about to fail.”
“Forensic experts looked for telltale patterns in the soil samples to determine whether the vehicle had been driven through the field recently.”
“When you tap the mic input button (which now has the telltale AI sparkle), you get a feature called Rambler.”
From tell + tale, perhaps dissimilated from earlier taleteller, from Middle English tale tellere (literally “tale teller”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.