How do you multi-texture something for the following effect
This is what I want to do. I want to do a glass texture with an etched/painted on logo.

I know how to do a glass material, but do I have to duplicate area for the decal and transparency it onto the glass (thus upping my quads) or can I “Layer” my materials together?

jonathon williamson has a decal tutorial on
this would explain what your trying to do.

Okay, have now seen the empty application, but is there no other way?

It can just remain 1 material, and the logo is an image texture influencing anything you need for the effect (color, transparency, specular,…).

How you apply the texture can be in different ways: map to empty, UV unwrap,…

Do you know of any tutorial to explain that?

Make a glass like material. Then use gimp or photoshop to make the logo texture you need and make it have an alpha channel(Remember to save it as .png). Use UV Unwrap to place it where you need. Also make sure you set the logo texture to influence alpha values.