The sign says that the shop was "Formerly Chuck's", implying that the two words beginning with "F" and "S" would have ended with "-uck", rhyming with "Chuck". So, when Chuck owned the shop, it would have been called "Chuck's Fuck and Suck".
The sign is a subtle joke. The shop is called "Sneed's Feed & Seed", where feed and seed both end in the sound "-eed", thus rhyming with the name of the owner, Sneed.
