With all due respect to your ping list;
UNITED STATES CODE
§176. Respect for flag
(g) The flag should never have placed upon it, nor on any part of it, nor attached to it any mark, insignia, letter, word, figure, design, picture, or drawing of any nature.
It represents the solidarity the Serbs have with freedom and the toll they paid in blood fighting for it. With all due respect, the 500 US airman that were rescued by the Serbs who sacrificed their lives to protect them would gladly ignore this.