When is JWTSecurityTokenHandler.ValidateToken() actually valid?

I am attempting to create a token validation method that returns true if a JWT token is valid based on the signature. I don't think I really need to validate everything in the token but what actually signifies a token is valid after calling ValidateToken()? The existence of a principle? The out referenced token contains certain values? Not sure when to return true from this method.

public bool ValidateToken(string tokenString){    var validationParameters = new TokenValidationParameters()    {        ValidIssuer = "My Company",        ValidAudience = ApplicationId,        IssuerSigningKey = JsonWebTokenSecretKey    };    SecurityToken token = new JwtSecurityToken();    var tokenHandler = new JwtSecurityTokenHandler();    var principal = tokenHandler.ValidateToken(tokenString, validationParameters, out token);    return principal != null;}