A favicon is the image that appears next to the title of the page in your browser. Adding a favicon that matches the brand of your normal website adds consistency and credibility to your landing pages. It is easy to add a favicon to any individual landing page, as well as to a landing page template.
To add the favicon to an individual landing page or to a template, you will need this code:
<link rel=”SHORTCUT ICON” HREF=”the url to your fav icon goes here”>
When adding the favicon to a landing page template, simply paste the link code from above (with your favicon URL) into the template HTML immediately after the open <head> tag.
When adding a favicon to an individual landing page, paste the link code from above into the “Custom HEAD HMTL:” area of the edit meta tags section of the landing page actions drop-down.
Edit Draft > Landing Page Actions > Edit Meta Tags > *Paste link code into “Custom HEAD HTML” block.
You can pull the link for your favicon that is already on your website by viewing the page source of your company’s website and searching for the rel=”SHORTCUT ICON” portion of the code above. Once you find the link code, copy it in its entirety or copy just the URL portion to paste into the code provided above.
Source: Marketo Community