[szarnyasg]

Maybe they meant this paper?

Daniel Oppenheimer et al.: Fortune Favors the Bold (and the Italicized): Effects of Disfluency on Educational Outcomes (Proceedings of the Annual Meeting of the Cognitive Science Society, 2010), https://escholarship.org/uc/item/4wd1s7hj

"Study 1 found that harder to read fonts led to increased retention in a controlled laboratory setting. Study 2 extended this finding to real-world classroom environments."

I'm not an expert on this topic, so I don't know whether this result was replicated since. If it indeed works, then kudos to my university's physics department for making use of this effect - they had a habit of handing out physics cheat sheets and various MATLAB code snippets that have been photocopied for 15+ years from one copy to another.