(A). A perambulating advertisement displayer, with an advertisement board before and behind.
“The Earl of Shaftesbury desired to say a word on behalf of a very respectable body of men, ordinarily called `sandwiches.' ” —The Times, March 16th, 1867.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Sandwichman from Infoplease: