这边简单的设置一下placeholder的字体
//创建属性字典
var attributes:[String:AnyObject] = NSMutableDictionary() as! [String:AnyObject]
attributes[NSFontAttributeName] = UIFont.systemFontOfSize(13)
//创建带属性的字符串
let string:NSAttributedString = NSAttributedString.init(string: "身份证号中含字母必须大写", attributes: attributes)
//设置placeholder的属性
self.cardId.attributedPlaceholder = string