query: SELECT ?letter ?letterLabel (COUNT(DISTINCT ?character) AS ?count) (SAMPLE(?character) AS ?sample)
  WHERE
  {
    ?letter wdt:P31/wdt:P279* wd:Q9788;
            p:P487/ps:P487 ?character.
    SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
  }
  GROUP BY ?letter ?letterLabel
  HAVING(?count > 2)
  ORDER BY DESC(?count)