Methods and systems that provide privacy of signatures on envelopes containing ballots are provided. The envelope for returning ballots includes a flap with a window that aligns with a signature area on the envelope. The window appears opaque under normal lighting conditions, but appears transparent when illuminated with light having a predetermined wavelength. A movable signature stub is positioned on top of the signature area. The voter signs the back of the envelope on the signature stub, thereby imprinting a signature on the signature area by transferring a material from the signature stub to the signature area, and moves the signature stub. The flap of the envelope is then sealed, thereby covering the voter's signature in the signature area with the window of the envelope flap. To read the signature, light having the predetermined wavelength can be directed onto the window, thereby rendering the window transparent and the signature visible.