Green’s Dictionary of Slang

1. (US) a drinker.

1856

Spirit of the Times (NY) 29 Nov. 211/1: Tom Tit, a very ugly customer, [...] made straight for the bar-room and scattered all the smilers, and knocked their glasses into a thousand sparkles [DA].

2. a form of shandygaff, a mixture of beer and ginger beer.

1892

Daily News 16 Nov. 2/3: A singular mixture of beer and lemonade known in Manchester as a smiler.

3. stout and lemonade.

1902

Dundee Courier 14 June 7/2: A ‘smiler’ means a lemondade with a dash of stout.