  Electromagnetic skins (EMSs) have been recently considered as a booster for
wireless sensing, but their usage on mobile targets is relatively novel and
could be of interest when the target reflectivity can/must be increased to
improve its detection or the estimation of parameters. In particular, when
illuminated by a wide-bandwidth signal (e.g., from a radar operating at
millimeter waves), vehicles behave like \textit{extended targets}, since
multiple parts of the vehicle's body effectively contribute to the
back-scattering. Moreover, in some cases perspective deformations challenge the
correct localization of the vehicle. To address these issues, we propose
lodging EMSs on vehicles' roof to act as high-reflectivity planar
retro-reflectors toward the sensing terminal. The advantage is twofold:
\textit{(i)} by introducing a compact high-reflectivity structure on the
target, we make vehicles behave like \textit{point targets}, avoiding
perspective deformations and related ranging biases and \textit{(ii)} we
increase the reflectivity the vehicle, improving localization performance. We
detail the EMS design from the system-level to the full-wave-level considering
both reconfigurable intelligent surfaces (RIS) and cost-effective static
passive electromagnetic skins (SP-EMSs). Localization performance of the
EMS-aided sensing system is also assessed by Cram\'er-Rao bound analysis in
both narrowband and spatially wideband operating conditions.
