In each theme I make, I always give a signature in the form of links to my websites. I do not require you to leave these links, it is voluntary and you are free to remove it in your website.
I am grateful for those who leave these links, or at least you leave one link to my website. Because with this links, then people get to know who made the theme and people will know the services I provide.
You can modify the links so that according to your website.