It is obvious that self-adhesive stamp can made in flexible shapes. This banana stamp is from Tonga, where the world first self-adhesive stamp was issued from. This one is clearly inspired by the commercial stickers which are used for showing the origin of fruits – this is why it is very small, end to end is about 2.5 cm.
I would be very pleased to receive a letter with this stamp from Tonga. They are now exporting a lot of pumpkins to Japan.