  We investigate the properties of multiple-image gravitational lens systems
formed by dark matter halos. Both the Navarro-Frenk-White (NFW) and Moore et
al. mass profiles are considered, and the effects of quadrupole perturbations
to the lensing potential are taken into account. The systems produced by dark
halos exhibit two generic properties that serve as powerful benchmarks for
scrutinizing individual lens candidates: small flux ratios between the two
brightest images in triples, and detectable odd images. In contrast, most
currently ambiguous quasar pairs consist of two components with flux ratios >
3:1. Such systems are statistical outliers in the expected distribution of dark
lenses, and are therefore likely to be binary quasars.
