The Collaborative International Dictionary of English v.0.48:

Flash \Flash\, a.
   1. Showy, but counterfeit; cheap, pretentious, and vulgar;
      as, flash jewelry; flash finery.
      [1913 Webster]

   2. Wearing showy, counterfeit ornaments; vulgarly
      pretentious; as, flash people; flash men or women; --
      applied especially to thieves, gamblers, and prostitutes
      that dress in a showy way and wear much cheap jewelry.
      [1913 Webster]

   Flash house, a house frequented by flash people, as thieves
      and whores; hence, a brothel. "A gang of footpads,
      reveling with their favorite beauties at a flash house."
      --Macaulay.
      [1913 Webster]