For Mums birthday I gave her an IOU for tickets to tour the Harry Potter set. She's wanted to go for ages but felt guilty as I'm a huge Harry Potter fan but too ill to even consider going. As I didn't have the actual tickets to give her I did a special letter instead.
I've not tea bag stained anything since I was at school but used a wet tea bag to make a piece of paper look like parchment, while still wet I sprinkled a few grains of coffee on. Then I wrote in green pen as Dumbledore himself wrote in green and added a red seal with a H on the back. On the front it had Mums name and our address but with 'master bedroom' added.
The letter said;
To Mrs D George
Happy Birthday. You are invited to Hogwarts. Sadly you are past the age limit to be a student, your too tall to be a house elf and have CSE's instead of OWLs so can't be a teacher.
Due to this we are inviting you following a bribe from Vikki. You will walk down Diagon Alley, enter the Great Hall and see Hogwarts from dawn to dusk.
Vikki will also bribe us to give you the devices to hear about what your seeing,
Enjoy your visit,