  We analyzed images of every northern hemisphere Sd galaxy listed in the Third
Reference Catalogue of Bright Galaxies (RC3) with a relatively face-on
inclination ($\theta\leq30{\deg}$). Specifically, we measured the spiral arms'
winding angle, $\phi$, in 85 galaxies. We applied a novel black hole mass
planar scaling relation involving the rotational velocities (from the
literature) and pitch angles of each galaxy to predict central black hole
masses. This yielded 23 galaxies, each having at least a 50% chance of hosting
a central intermediate-mass black hole (IMBH),
$10^2<M_\mathrm{BH}\leq10^5\,\mathrm{M}_\odot$. These 23 nearby ($\lesssim$50
Mpc) targets may be suitable for an array of follow-up observations to check
for active nuclei. Based on our full sample of 85 Sd galaxies, we estimate that
the typical Sd galaxy (which tends to be bulgeless) harbors a black hole with
$\log(M_\mathrm{BH}/\mathrm{M}_\odot)=6.00\pm0.14$, but with a 27.7% chance of
hosting an IMBH, making this morphological type of galaxy fertile ground for
hunting elusive IMBHs. Thus, we find that a $\sim$$10^6\,\mathrm{M}_\odot$
black hole corresponds roughly to the onset of bulge development and serves as
a conspicuous waypoint along the galaxy-SMBH coevolution journey. Our survey
suggests that $>$1.22% of bright galaxies ($B_{\rm T}\lesssim15.5$ mag) in the
local Universe host an IMBH (i.e., the "occupation fraction"), which implies a
number density $>$$4.96\times10^{-6}$ Mpc$^{-3}$ for central IMBHs. Finally, we
observe that Sd galaxies exhibit an unexpected diversity of properties that
resemble the general population of spiral galaxies, albeit with an enhanced
signature of the eponymous prototypical traits (i.e., low masses, loosely wound
spiral arms, and smaller rotational velocities).
