You should sign it. And btw if you're ready to sign your drawings, make sure the signature covers the whole drawing, so people can't crop the signature part away
You don't "have" to do anything. But signing your drawings is never a bad thing. If you don't like the look of your signature being on the front than perhaps at least sign the back.
I didn't realize you were talking about digital artwork or drawings that are scanned an published online. In that situation you should add a large signature watermark. IMO