Many pritner's software has a watermark feature
I'm not sure the watermark can be a picture, but it can definitely be text
If you're using windows, go to printers and faxes (normally found in the start menu) Then click the default printer right click, and printing preferences. Go to advanced TAB and somewhere there should be a watermark option.
This is true in most printers, although i dont know what yours is.
Also you could create a template with whatever document you are making, to automatically put your signiture on every new document you create
