* They're always outside howling at the full moon. It's a classic werewolf sign, though maybe they just have a really loud dog.
* They have an unusual amount of hair on their body. You see them in their garden and notice an abundance of body hair, even for a hairy person.
* They're always wearing a lot of dark, loose clothing. This could be a way to hide any potential transformations.
* They're constantly complaining about the smell of blood. Maybe they have a sensitive nose, or maybe they're covering up their own blood lust.
* They have a sudden aversion to silver. This is a well-known werewolf weakness. Maybe they get unusually agitated if you mention silver or have a silver object in their presence.
* They disappear on nights of the full moon and reappear with unexplained injuries. You might see them leave their house at night and come back the next day with scratches and bites.
Remember: These are all very unlikely reasons to believe someone is a werewolf. If you're worried about your neighbor, it's best to talk to them or contact the authorities if you have a genuine reason.