CREATE TABLE table_203_657 (id DECIMAL, "call sign" TEXT, "frequency" TEXT, "city of license" TEXT, "licensee" TEXT, "format" TEXT)

which cities have at least three call signs ?
SELECT "city of license" FROM table_203_657 GROUP BY "city of license" HAVING COUNT("call sign") >= 3
SELECT "city of license" FROM "table_203_657" GROUP BY "city of license" HAVING COUNT("call sign") >= 3