I dont know why you would want this?? Anyway, create new User Control and add a label on it, then, in the code behind add a Text property:
private string _text = string.empty;
public string Text
{
get
{
return _text;
}
set
{
_text = value;
lblMyLabel.Text = "";
foreach(char c in value)
lblMyLabel.Text += "*";
}
}
Then you just add that user control to your page I guess! Thats if I am understanding your question.