I don't believe so. But like Jason said, there are certain traits that stick out. Usually physical traits and personality traits. Most half-bloods have a lot of the same physical traits as their Olympian parent (though not always).<br/><br/>Children of Ares tend to be rougher, meaner, easily angered. They also tend to have a warrior's body.<br/>Children of Hermes tend to have more sharp features (pointed noses, chins, ears) that make them look sneaky. They are also good at Track and Field type sports.<br/>Children of Hades have dark features (dark hair and eyes, but pale skin), and almost feel cold to be around.<br/>Children of Hephaestus usually look a bit rough or well worked. They also always like getting their hands dirty and building things.<br/><br/>Things like that. So while they don't always 'look' like a sibling, personality traits, hobbies, etc...will tend to match up.