The bronze trophy from the hunting tasks are writable so I can only assume the others are aswell. They cost a certain amount of points if you'd like to purchase one.
Bronze Hunter Trophy - 3000 Hunting Task Points
Silver Hunter Trophy - 15.000 Hunting Task Points
Gold Hunter Trophy - 80.000 Hunting Task Points
These also somewhat count as a TibiaStore item (When you wrap it it'll go to your store inbox), which also means that if you put them in your house no other player can pick them up/steal them.
Now to my point, I know that you can write on them, but are they re-writeable? If they are not then what happens when you wrap it back to your store inbox? Do they save whatever text you typed on it for when you unwrap it again?