I have seen a lot of posts on this subject, today I will show you how to add a search lens in the navigation bar (in the header) in Squarespace 7 using the tutorial made by the Squarespace Guru for Squarespace 6, that you can find here
This is how it looks like:
You will need to follow these steps:
1) Retrieve the search address for your Squarespace site, every Squarespace site has one.
• If you have a custom domain it will be as follows: www.yourdomain.com/search
• If you do not have a custom domain linked to your site, it will be as follows: www.yourusername.squarespace.com/search
2) Add in the Code Injection, in the header section the following code in Settings >> Advanced >> Code Injection >> Header:
<link href="//maxcdn.bootstrapcdn.com/font-awesome/4.1.0/css/font-awesome.min.css" rel="stylesheet">
This video shows you how to do it:
3) Add a link under the main navigation and name it the following:
<i class=" fa fa-search"></i>
Here is the video that shows you how to do it in Squarespace 7:
As a note, it might take a few minutes for the lens icon to display.
SOURCE: Squarespace Guru