Add Outline / Sticker Effect

[Ofnuts]

My technique:

1. Get a path on the initial text (if still a text layer,  Layer>Text To path, otherwise, Layer>Transparency>Alpha to selection to get a selection and then Select>To path|
   
2. Add a new transparent layer, remove the selection if any, and Edit>Stroke path in Line mode, with line width= twice the distance of the sticker border. At that point you can also choose if the sticker has pointy  or only round/beveled corners This will give you a very "fat" outline of your text., 
   
3. On that outline layer: Layer>Transparency>Alpha to selection, and then Select>To path
   
4. Add a new transparent layer, remove the selection, and Edit>Stroke path in Line mode, with a small line width (1-3 pixels)
   
5. You may need/want to clean off the resulting drawing f you don't want "holes" in the layer (like in the capital C's below)