Once you have finished a new work make sure that you sign it either on the front or the back.
Signing an artwork signifies that the artwork finished and that you as the artist approve of the finished artwork. Your signature is not an afterthought - it is a required part of the artwork.
As your career develops, NOT signing an artwork can lead to all sorts of problems. When someone looks at your art years from now, a signature will help to identify the artist and confirm that the work was created by you.
Make sure to sign all of your artwork in the same way. The signature should be consistent in size, style, and location on the artwork. And try to make your signature legible!