Elena L. from Google posted a help thread in the Google Webmaster Help forums about how some publishers may not be using the proper specifications for implementing the AMP logos. She said Google noticed a nice number of publishers incorrectly implementing them.
We’ve noticed that some publishers have not included a valid AMP logo in their AMP pages, or have implemented it incorrectly in their structured data markup. As a result, they will show no or only a low quality logo in the Google Search “Top Stories” carousel. This has a negative impact on a publisher's brand as well as the user experience on Google Search. Watch out for the common logo mistakes listed below and find out how to fix them.
These are the comment issues:
- Missing Logo Target : How to fix? Specify a logo value in the logo.url field of the AMP page’s structured data markup.
- Broken Logo Link: How to fix? Specify a logo value with a valid absolute URL in the logo.url field of the AMP page’s structured data markup.
- Square Logo Format: How to fix? Follow the general Logo guidelines. If your site uses a Content Management System (CMS) with a default square logo, check if they offer any options to override it.
- Illegible Logo: How to fix? Use a logo version with darker text or imagery to provide enough contrast against a white background. However, refrain from including a dark background in the logo itself to make the light items stand out. Ensure that the logo text or images are not too dense to be legible when viewed at their display size in the carousel.
You can test them at the structured data testing tool.
For example, here is a direct link to the Search Engine Roundtable logo for AMP.
Here is a photo of how it looks:
Forum discussion at Google Webmaster Help.