Sina,
There is a few things you can do ..
1. Wilton has letters that you press in to your cake and then you trace over them with your frosting...
2. You can take and find a font you like on your computer and write out what you want and then print it place a piece of wax paper over the top of the paper and copy with royal icing and let it harden and then place them on the cake... You would have to do this about 4-7 days ahead of your cake so they dry..
3. You can take and print out the paper from the computer in the font you like place a piece of wax paper on top of the page and then take clear piping gel and trace what you want it to say and then your going to flip the wax paper on to the top of your cake and softly rub your hand on the lettering and pull the wax paper off and then your going to trace over the piping gel with your frosting..
I hope these tips help you ..
Edited By: Victoria

Sorry I repeated what Jackie said there was not anything here at the time of me reading this message..