If a tail seat is the same as an orchard tractor the decal the normally goes on the back of the seat was put on the firewall.
The decal that normally goes on the side of the seat goes on the side of the hood.
I think the Caterpillar ten photo archive book has a couple of photos of a fifteen. The Caterpillar pocket guide has a photo of a "PV15 Orchard" on page 111. It shows the hood decals but does not really show the firewall decal location. Good luck!