  We present observations of three protoplanetary disks in visible scattered
light around M-type stars in the Upper Scorpius OB association using the STIS
instrument on the Hubble Space Telescope. The disks around stars 2MASS
J16090075-1908526, 2MASS J16142029-1906481 and 2MASS J16123916-1859284 have all
been previously detected with ALMA, and 2MASS J16123916-1859284 has never
previously been imaged at scattered light wavelengths. We process our images
using Reference Differential Imaging, comparing and contrasting three reduction
techniques - classical subtraction, Karhunen-Loeve Image Projection and
Non-Negative Matrix Factorisation, selecting the classical method as the most
reliable of the three for our observations. Of the three disks, two are
tentatively detected (2MASS J16142029-1906481 and 2MASS J16123916-1859284),
with the third going undetected. Our two detections are shown to be consistent
when varying the reference star or reduction method used, and both detections
exhibit structure out to projected distances of > 200 au. Structures at these
distances from the host star have never been previously detected at any
wavelength for either disk, illustrating the utility of visible-wavelength
observations in probing the distribution of small dust grains at large angular
separations.
