Smart App Banners have been around since iOS 6 and are an easy way for websites to link to apps on the App Store. As app promotion methods go, these are intelligent and not as obtrusive as other methods.
To add them to your page you have to add a meta tag to the head of each page where you want the banner to appear. I wanted to add a banner to our Avoid Town page but on Squarespace you don't have access to the raw HTML. However you can provide custom Javascript.
First go to the page you want the banner to appear on and click on the gear icon to access the page's settings.
Now click on Advanced at the top right of the page and you'll be presented with a textarea where you can enter code to be injected into the page.
Next paste in the code below, replacing XXX with your app's ID and YYY with your iTunes affiliate ID (or leave it blank).
You can find your app ID using the iTunes Link Maker and if you haven't you should join the iTunes Affiliate Program.