This is actually an interesting question ---- offering "proofs" is a routine task, and here is the way to accomplish it:
1. Drawing a thin border around your design is a good thing to do, because it keeps the design within parameters of the sign shape you are making, instead of just floating in empty space.
2. Select All, and then go to FILE - EXPORT and at the bottom (File type), choose the .jpg option.
3. Give it a name, and a location to store it. Hit SAVE.
4. Choose a size (make it relatively small, like 200 or 400 pixels)