The flag of Serravalle, San Marino.
<div style="display:inline-block;padding:0 3px;background-color:#CCF">Original:</div> <div style="display:inline-block;padding:3px 0;"><a href="//commons.wikimedia.org/w/index.php?title=User:Nickel_Chromo~commonswiki&amp;action=edit&amp;redlink=1" class="new" title="User:Nickel Chromo~commonswiki (page does not exist)">Nickel Chromo~commonswiki</a></div> <div style="display:inline-block;padding:0 3px;background-color:#CCF">Vector: </div> <div style="display:inline-block;"><a href="//commons.wikimedia.org/wiki/User:DraftSaturn15" title="User:DraftSaturn15">DraftSaturn15</a></div>
CC BY 2.5
Own work based on: <a href="//commons.wikimedia.org/wiki/File:Castello_di_Serravalle.jpg" title="File:Castello di Serravalle.jpg">Castello di Serravalle.jpg</a>