  Despite strong experimental evidences for their conservation at low energies,
the baryon $B$ and lepton $L$ numbers are not expected to be absolute
symmetries. Already violated in the Standard Model (SM) by non-perturbative
effects (tiny at low temperatures and energies) and not justified by any
fundamental principle, $B$ and $L$ appear naturally violated in beyond the
Standard Model (BSM) scenarios, e.g. in supersymmetry (SUSY). The fact that any
violation remained unobserved at low energies can nonetheless be explained,
without pushing the associated characteristic sale beyond the TeV, by using SM
flavour symmetries implemented BSM thanks to the Minimal Flavour Violation
(MFV) prescription. Violation effects could therefore be observable at the LHC.
Same-sign (anti-)tops, sometimes leading to a distinctive predominance of
negatively charged lepton pairs over positively charged ones, is a clean
signature that is for instance generically present in R-parity violating
supersymmetry.
