Panel (A) shows a comparison of the normalized spectra of SN 2020uem and SN 2005gj (IIn/Ia-CSM; Silverman et al. 2012), SN 2010jl (IIn; Zhang et al. 2012), and SN 2017dio (peculiar Ic; Kuncarayakti et al. 2018). The missing parts of Hα are shown in the upper right panel. Panel (B) is the same as panel (A), but for PTF11kx (Ia-CSM; Dilday et al. 2012) and SN 1991T (Ia; Gómez & López 1998). All spectra are normalized by their continua using the Astropy package. All the spectra, except for SN 2020uem, are gathered from WISeRep. The spectral regions mentioned in the main text are highlighted with gray shaded areas.