  We investigate the possible presence of quasi-periodic oscillation (QPO)
signals in 2103 blazars from the Zwicky Transient Facility (ZTF) time-domain
survey. We detect a low-frequency QPO signal in five blazars observed over
these 3.8-year-long optical r-band ZTF light curves. These periods range from
144 days to 196 days detected at $\gtrsim 4\sigma$ significance levels in both
the Lomb-Scargle periodogram and Weighted Wavelet Z-transform analyses. We find
consistent results using the phase dispersion minimization technique. A similar
peak is detected in the g-band light curves at a slightly lower significance of
3$\sigma$. Such nearly periodic signals on these timescales in optical
wavebands most likely originate from a precessing jet with high Lorentz factor,
closely aligned to the observer's line of sight or the movement of plasma blobs
along a helical structure in the jet.
