。
Please don't forget to sign, okay?
Literal
Not-forget-[without-ず] signature [object-を] do-[polite-request-てください] [tag-ね]
Notice 署名をする ('do a signature') rather than a single verb meaning 'to sign' — Japanese frequently uses する with a Sino-Japanese noun to make a verb. The final ね gently softens the polite request.