I was at the Met yesterday, where by chance I ran across the Concinnitas Project.
You can read about it in the placard above; the project asked several well-known mathematicians to indicate which mathematical expression they found the most beautiful, including David Mumford (whose expression is pictured above), Sir Michael Atiyah (who submitted the index formula), Freeman Dyson, and so on. Mumford's submission is his formula for the canonical bundle of \(\mathscr{M}_g\), namely that it is the 13th power of the determinant of the Hodge bundle. (In fact he computes the canonical class of \(\overline{\mathscr{M}_g}\), but perhaps he felt that this was beyond the scope of the Met.)
Other weird stuff now on view at the Met includes this embalmed deer, encased in giant glass bubbles:
