You can sometimes tell someone is wearing a wig, but the better question is why you need to know. Hair can be fashion, privacy, medical recovery, religion, performance, or protection.
Common giveaways
A too-perfect hairline, heavy density at the part, visible lace edge, unusual shine, or a cap that shifts can make a wig noticeable.
Why good wigs are harder to spot
Modern lace, rooted colors, realistic density, and better cap fit make many wigs blend beautifully. A natural-looking wig has variation, not perfection.
Respect matters
Do not touch, pull, joke, or announce your suspicion. If someone wants to talk about their wig, they will.
Bottom line
Yes, there are clues. But noticing a wig is not an invitation to comment on it.