During the Renaissance, hand gestures in art were as important as faces, conveying secrets, codes, and messages. An unusual hand gesture with tight third and fourth fingers and separated second and fifth fingers puzzled experts. The gesture was not related to known symbols like Masonic signs, religious gestures like Loyolan penance, or hand recognition among the Marranos. It was not an accidental depiction or a sign of syndactyly, rather an artistic trend to portray elegance and refinement. While the true meaning remains speculative, it was more likely a symbolic hallmark in art rather than a medical anomaly.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7233791/