NP, you can solve the problem with your initial setup. Here's the step-by-step:

1. Create your two surface materials...one for the white porcelain surface of the cup and one for the cobra label. You can also create your layered shader for later use.

2. Create your cobra texture in photoshop with an alpha channel and save out as targa or tif.

3. Load the file texture (as normal, not projection) into your label material's color attribute. Make sure it only goes to the color attribute as I think Maya's default is to connect both color and transparancy if it sees an alpha channel. If that's the case, delete the connection to transparancy. Go ahead and assign the label material to your mug. The texture should be covering the whole mug object.

4. Click on the file texture's 2D placement node and choose interactive placement. Click on the mug and you should see a red curve with u and v and various points for selecting. This can get a bit tricky, but mmb + click/drag on the various points you see on that to place your cobra texture where you want it. I usually use this to adjust the label's height and how much it wraps around the object. If the cobra is upside down, go into the 2D texture node's attributes and rotate it or the UVs...whatever works.

5. Ok, when you've fine-tuned the placement of the cobra label, go into the file texture node's color balance > default color and change it to white. Next we're going to set up its transparency.

6. shift +mmb + drag and drop the file texture node on top of the label material. This will open the connection editor. Connect the Out Alpha to Transparency rgb values. You should now just see your cobra label if you do a render.

7. Now we can start hooking things up to the layered shader. MMB + drag the label material on to the layered shader's color attribute. Click once in the layer area to create another layer. Now mmb + drag the other material (the white porcelain mug surface) onto the color attribute for the new layer. If you render you still won't see a change so we can fix this with another connection.

8. MMB + shift + drag/drop the file texture node on top of the layered shader node. This time connect Out Alpha to Inputs [0] transparency RGB.

9. That should be it. Assign the layered shader to your mug and see what happens. I've attached a simple scene for you to look at using the above method.

Good Luck!