How to add custom signature on every post

Hello, I want to add after everypost my specific signature along with a small javascript that makes a little nice effect and every week i change my signature how can i make a small sort of variable that i can add on the end of my every post and whatever new signature i make to be automatically added to all my posts.

Example:

Title: blabla bla

Post: Hello World
and here at the end to add
[signature]

and this [signature] to show what i have set as signature for that week and display it?

I hope you understood what I mean.

Thank you very much and have great holidays!

Find <b:widget id='Blog1'
at the bottom of the code place your script or code and save the changes.
Without your template code can't say where or how to place your code, and what code you need to place. (Please read the forum guidelines before post, and provide as much information as you can)

Also a easy way to perfor the same task without mess with the template code s to create a HTML widget at the bottom of the post area, in that way you can change your signature in just a couple of seconds.

Sorry for my english