Hmm I'm not really sure what you mean about it 'being on'?
If there is any sort of text in the 'Edit Signature' part of your settings it should just be 'on', and should display what is in there.
There's no way of toggling it on and off (to my knowledge, anyway) unless you go into Advanced Settings every time you post and specifically disable your signature for each post.
What do you want to be in your signature? Maybe if you put a link to an image in this thread that you'd like I could send you the code to make it show up in your signature?