Unless in exceptionally high original condition or a very high grade --
not much.
The company began in 1865 as E. Allen & Co. From 1871 to 1890 it was Forehand & Wadsworth, and from 1890 to 1902 Forehand Arms Co. The hammerless double was introduced by Forehand Arms Co. in 1892, and made in four grades -- 0, 1, 2 and 3. Forehand Arms Co. was taken over by Hopkins & Allen Arms Co. by 1902 and H & A marketed the doubles for a couple of years as the "New Forehand." From the 1902 H & A catalogue --
By 1908 they had simplified the profiling of the receivers a bit were calling them the Hopkins & Allen Hammerless Double Gun.