DYMO's One-Day Self-Expiring Security Stickers come in two parts. The "front part" labels are marked with the letter 'V'. The "back part" labels are marked with a grid of crossing lines. To use a Security Sticker (and start the one-day expiration process), peel off a "front part" label and place it on top of a "back part" label. After 24 hours, the grid from the "back part" label will bleed completely through and become highly visible, obscuring the letter 'V' on the "front part" label.