Large Thorny Heart Tantoo Tanning stickers are a great way to measure your tan. It is always hard to see your own tanning progress by looking in the mirror. Tanning is a process and therefore your color changes throughout the day and from one day to the next. The only effective way to measure your tanning progress is to use a tanning sticker in the same spot each time you tan. Almost everyone is surprised by how tan they actually are once they have used a thorny heart sticker for a few weeks.