I'm a web designer with some ideas but not sure how to approach them.
I make free web templates, just basic HTML and CSS templates and I'm looking for an idea/help for a way to have my templates display a small ad/copyright within the template that can't be easily edited or removed from the template to promote my company. But at the same time isn't intrusive such as a popup ad etc.
One example idea I have, was to have the css prehosted for them, leaving them with the html file to be edited as necessary. Within the CSS file, I had a few certain divs that would hold a simple background image with the name of my company, and be displayed within the template.

Another idea/example of what i'm trying to achieve as close as possible without going overboard.
I'm not sure if I'm allowed to link to websites to examples but I'll name a few of what I mean. Wixdotcom is a website you can design websites free, and after you do so, they put a little clickable banner on the website saying it was designed free from their website, and click here to make your own. This is basically what I want to achieve but in the most simple form. Basically a way I can host a small portion of the template which will be hosted on my server that will show some sort of advertisement back to my website within each free template I provide. I hope this is a bit more clear of what I'm trying to achieve.

Any ideas, comments, examples I would much appreciate. I really don't want all my hard work being giving out for free to be just left without any sort of acknowledgment to my company. Thanks in advanced.