Fiddle: http://jsfiddle.net/LkqTU/9399/
Code:
var ViewModel = function (first, last) { var self = this; self.showIcon = ko.observable(false)
Addendum to @RP Niemeyer's answer...
On github there is a small project called Knockout-Bootstrap for making "rich two way interactions with Bootstrap and Knockout bindings".
Below is a fork of your fiddle that includes Knockout-Bootstrap.
http://jsfiddle.net/qZkXP/