Bobbin Girl (for the exclusive Handcrafted in Great Britain ones) or Emmaline bags for US, Canada & Australia labels. Emmaline also carry the Great Britain ones, but if you're in the UK, you'll prefer UK postage times, right?
First you should lay the bag label face down where you think you want it. I chose to put mine on my nappy bag so I laid the pocket on the wrong side and then placed my label. Mark the top and side of the label.
You can see that I've marked the centre of my main panel as the pattern calls for this. It's really handy for placing a bag label on centre as well.
You could of course use these labels on anything, but I think they look great on bags! Just make sure your outer is sufficiently stabilised to take the weight of the label without sagging!