This is a short video of creating a signature for a brass stamp. https://www.youtube.com/watch?v=6SphFcky2_M
Best file formats for images are .ai, .eps, .pdf. Vectored formats with outlined fonts.
Next is high resolution (300dpi) graphic files like .png and .jpg or jpeg.
A Screen shot of your work in as large a window as possible. Closeup picture with your cell phone and email it to firstname.lastname@example.org.