  Continuous gravitational-wave signals (CWs) are long-lasting
quasi-monochromatic gravitational-wave signals expected to be emitted by
rapidly-rotating non-axisymmetric neutron stars. Depending on the rotational
frequency and sky location of the source, certain CW signals may behave in a
similar manner to narrow-band artifacts present in ground-based interferometric
detectors. Part of the detector-characterisation tasks in the current
generation of interferometric detectors (Advanced LIGO, Advanced Virgo, and
KAGRA) aim at understanding the origin of these narrow artifacts, commonly
known as ``spectral lines''. It is expected that similar tasks will continue
after the arrival of next-generation detectors (e.g. Einstein Telescope and
Cosmic Explorer). Typically, a fraction of the observed lines in a given
detector can be associated to one or more instrumental causes; others, however,
have an unknown origin. In this work, we assess the similarity of CW signals to
spectral lines in order to understand whether a CW may be mistaken for a noise
artifact. Albeit astrophysically unlikely, our results do not rule out the
possibility of a CW signal being visible in the detector's power spectrum.
