When Zoro fought Mihawk in the East Blue, Mihawk asks Zoro his name, then when Zoro attacks him with his “secret technique”, he has a look of surprise, as if he’d seen this move somewhere before.
Mihawk clearly saw through his technique, there was no particular reason to be so surprised and scared.
After the fight, he thanks Luffy for taking care of Zoro and tells Zoro to find his “true self” and his “true world”.
I’m not too clear on this, but since some of Zoro’s secret moves seem to originate from Wano such as “Asura”, and Zoro’s “Snatch” connection to Wano in the latest chapters, I think that Mihawk realized that Zoro is from Wano when he saw that technique.
I know this might be a reach, but that Mihawk panel always intrigued me and I think it has a deeper meaning than “realizing Zoro’s potential”.
*Theory by aliassum