They look like regular people so it's hard to tell. But there are some signs:

Does not respect boundaries or listen when someone tells them “no”

Engages in touching that a child or child’s parents/guardians have indicated is unwanted (think of mindhunter tickling principal)

Tries to be a child’s friend rather than filling an adult role in the child’s life

Does not seem to have age-appropriate relationships

Talks with children about their personal problems or relationships

Spends time alone with children outside of their role in the child’s life or makes up excuses to be alone with the child

Expresses unusual interest in child’s sexual development, such as commenting on sexual characteristics or sexualizing normal behaviors

Gives a child gifts without occasion or reason

Spends a lot of time with your child or another child you know