Just a hint... half an em is an en (printing spaces). So remove an N from a word for symbol, which is probably SIGN, giving SIG. Add PRAWN or maybe SHRIMP to SIG, anagram it and...you may get a placename. Of course there are countless other shellfish...
Is this too cryptic?: Take the acronym HANE (heredidary angioneurotic oedema) as a symbol, less the N (being half a printers M) gives HAE and to Shrimp and mix to get Hampshire.