People, who do not want to subclass the view (UILabel/UIButton) etc... 'forgetButton' can be replace by any lable too.
-(void) drawUnderlinedLabel {
NSString *string = [forgetButton titleForState:UIControlStateNormal];
CGSize stringSize = [string sizeWithFont:forgetButton.titleLabel.font];
CGRect buttonFrame = forgetButton.frame;
CGRect labelFrame = CGRectMake(buttonFrame.origin.x + buttonFrame.size.width - stringSize.width,
buttonFrame.origin.y + stringSize.height + 1 ,
stringSize.width, 2);
UILabel *lineLabel = [[UILabel alloc] initWithFrame:labelFrame];
lineLabel.backgroundColor = [UIColor blackColor];
//[forgetButton addSubview:lineLabel];
[self.view addSubview:lineLabel];
}