How to add your own signature if you use ThunderBird under Linux

Today I find you can add signature following this way:

1,use vi or other edit tool to build a empty file
2,write your signature in it and save it in any directory. It should be best to save it in .txt file.
3,open your thunderbird and do edit/Account Settings, you will see add signature file. Then you can add the txt file.
4,when you build a new email, you will see you signature now...