Most Normal Signatures have these things :
450x150 Pixels,
A render + Text or just Render/Text,
Some nice backgrounds made by special effects and brushes.
This is an example :
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To make a signature where the render pops out of the picture, you will have to do this :
1# Make background 450x150.
2# Add the render, but let it be too big for the background, so you can't see the whole render. (Not too much)
3# Make the background fit the render with colours.
4# Click on "Image" --> "Canvas size" --> "500x170"(or what ever your canvas need to make the render stay inside the whole canvas).
This is an example :
(I used 450x150 and then 600x150).