We are a web design and development Company. We create many site and we have lot of portfolio items.
Normally we put link in footer of sites for we developed as very small text. Some client and US don't like to pull it in some sites. They may ask to remove and in some site it wont look good so we don't prefer to put in all.
So can we add a link back to our site as display none or hidden property or font size 1? Is it a black hat SEO technique that Google don't like? Will they ban us?