The text is a variation of the expression 'Don't buy a pig in a poke,' which means not to buy something without first checking it. The phrase 'hold up the poke' suggests being cautious or inspecting the 'poke' (a bag or sack) before accepting the pig. It does not play on different meanings of a word or similar-sounding words for a humorous effect.
When the pig is proffered , hold up the poke .