Looks like you can do it a few different ways.
May want to try looking at some of these suggestions:
Edit:
You can do something like this in javascript:
$(window).scroll(function(){
var height = $(this).scrollTop();
var brand = $("#brand");
if (height > 100){
brand.show();
}
else{
brand.hide();
}
});
I have updated your jsfiddle with some changes: Fiddle It isn't completely working with layout included but it does what you are expecting. I added a div in your html with the id and class of Brand. I then set the background to the url you have for the logo. I also set it to hidden by default. When you scroll the logo should appear and disappear when you scroll back up to the top.