Button, 20th Regiment Bengal Native Infantry (1855-1857; plus re-raised from 20th Bengal Native Infantry, 1861-1877), 20th Bombay Native Infantry (1855-1877) and 20th Madras Native Infantry (1855-1877).  
French circle and dot, '20' in centre, wreath around.  No rim, brass.  Reverse marked Smith Kemp & Wright Birmingham. 
Collection of 21 buttons marked Indian Infantry Other Ranks. 
From the collection of Maj H G Parkyn.