  We use the SPHINX$^{20}$ cosmological radiation hydrodynamics simulation to
study how Lyman Continuum (LyC) photons escape from galaxies and the
observational signatures of this escape. We define two classes of LyC leaker:
Bursty Leakers and Remnant Leakers, based on their star formation rates (SFRs)
that are averaged over 10 Myr (SFR$_{10}$) or 100 Myr (SFR$_{100}$). Both have
$f_{\rm esc}>20\%$ and experienced an extreme burst of star formation, but
Bursty Leakers have ${\rm SFR_{10}>SFR_{100}}$, while Remnant Leakers have
${\rm SFR_{10}<SFR_{100}}$. The maximum SFRs in these bursts were typically
$\sim100$ times greater than the SFR of the galaxy prior to the burst, a rare
$2\sigma$ outlier among the general high-redshift galaxy population. Bursty
Leakers are qualitatively similar to ionization-bounded nebulae with holes,
exhibiting high ionization parameters and typical HII region gas densities.
Remnant Leakers show properties of density-bounded nebulae, having normal
ionization parameters but much lower HII region densities. Both types of leaker
exhibit [CII]$_{\rm 158\mu m}$ deficits on the [CII]-SFR$_{100}$ relation,
while only Bursty Leakers show deficits when SFR$_{10}$ is used. We predict
that [CII] luminosity and SFR indicators such as H$\alpha$ and M$_{\rm
1500\r{A}}$ can be combined to identify both types of LyC leaker and the mode
by which photons are escaping. These predictions can be tested with [CII]
observations of known $z=3-4$ LyC leakers. Finally, we show that leakers with
$f_{\rm esc}>20\%$ dominate the ionizing photon budget at $z\gtrsim7.5$ but the
contribution from galaxies with $f_{\rm esc}<5\%$ becomes significant at the
tail-end of reionization.
