  Mergers between helium white dwarfs and main-sequence stars are likely
common, producing red giant-like remnants making up roughly a few percent of
all low-mass ($\lesssim2M_\odot$) red giants. Through detailed modelling, we
show that these merger remnants possess distinctive photometric, asteroseismic,
and surface abundance signatures through which they may be identified. During
hydrogen shell burning, merger remnants reach higher luminosities and possess
pulsations which depart from the usual degenerate sequence on the asteroseismic
$\Delta\nu$--$\Delta\Pi$ diagram for red giant branch stars. For sufficiently
massive helium white dwarfs, merger remnants undergo especially violent helium
flashes which can dredge up a large amount of core material (up to
$\sim0.1M_\odot$) into the envelope. Such post-dredge-up remnants are more
luminous than normal red clump stars, surface carbon-rich, and possess a wider
range of asteroseismic g-mode period spacings and mixed-mode couplings.
Recently discovered low-mass ($\lesssim0.8M_\odot$) red clump stars may be core
helium-burning remnants of mergers involving lower-mass helium white dwarfs.
