All sites are apparently listed here without any distinction.
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
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From the list on that page, the icons on the left are the Release sites; on the right are Beta sites. Notice the similarity between all the Beta site icons:
It's got real graphics and the non-beta look.
As of the time of this writing the beta design always looks like:
Easy to spot quickly.