We analyse hadronically quiet trilepton signatures in the T-parity conserving
Littlest Higgs model and in R-parity conserving supersymmetry at the Large
Hadron Collider. We identify the regions of the parameter space where such
signals can reveal the presence of these new physics models above the Standard
Model background and distinguish them from each other, even in a situation when
the mass spectrum of the Littlest Higgs model resembles the supersymmetric
pattern.Comment: 14 pages, 4 figures, Latex; v2: a few comments and references added,
typos corrected, conclusions unchanged, version to be published in Physics
Letters