How do you lose the background in a signiture?
The easiest way is probably to select the Magic wand (fourth icon row on the tool selector).
Keep it pressed if not visible and select it in the expanded row.
Now tap on the part of the layer that does not have the signature.
Once selected you can delete it by pressing the Edit menu (pencil icon on the top bar) and press "Clear".
Hope it helps,
Ignacio
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