  Fracton phases feature elementary excitations with fractionalized mobility
and are exciting interest from multiple areas of theoretical physics. However,
the most exotic 'type-II' fracton phases, like the Haah codes, currently have
no known experimental diagnostics. Here, we explain how type-II fracton phases
with gapless gauge modes, such as the $\mathrm{U}(1)$ Haah code, may be
identified experimentally. Our analysis makes use of the 'multipole gauge
theory' description of type-II fracton phases, which exhibits
ultraviolet-infrared (UV-IR) mixing. We show that neutron scattering
experiments on gapless type-II fracton phases should generically exhibit exotic
pinch points in the structure factor, with distinctive anisotropic contours as
a direct consequence of UV-IR mixing. This characteristic pinch point structure
provides a clean diagnostic of type-II fracton phases. We also identify
distinctive signatures of the (3+1)-D $\mathrm{U}(1)$ Haah code in the
low-temperature specific heat.
