Werewolves are not something you can readily pick out, like albinos or others affected by something that makes them appear different from the rest of "normal" society.
Unless a werewolf makes himself known to you, in his human form, you would probably not give him a second look. But...if you observe closely you may pick up some traits such as increased nervousness on an approaching full moon, a change to eating meat more rare than before and a tendency to sniff the air on occassion.
These are small, but improtant details that could come in handy.
If they are part of a pack, there may be marks on the body or certain jewelery or clothing common to the pack members. The members will usually defer to the pack leader or alpha male when gathered in groups.
Keep your eyes open.