  The discovery of double-peaked light curves in some superluminous supernovae
offers an important new clue to their origins. We examine the published
photometry of all Type Ic SLSNe, finding 14 objects with constraining data or
limits around the time of explosion. Of these, 8 (including the already
identified SN 2006oz and LSQ14bdq) show plausible flux excess at the earliest
epochs, which deviate significantly (2-9$\sigma$) from polynomial fits to the
rising light curves. Simple scaling of the LSQ14bdq data show that they are all
consistent with a similar double-peaked structure. PS1-10pm provides
multicolour UV data indicating a temperature of $T_{\rm bb}=25000\pm5000\,$K
during the early `bump' phase. We find that a double-peak cannot be excluded in
any of the other 6 objects, and that this behaviour may be ubiquitous. The
homogeneity of the observed bumps is unexpected for interaction-powered models.
Engine-powered models can explain the observations if all progenitors have
extended radii or the central engine drives shock breakout emission several
days after the supernova explosion.
