Answer: one of the oldest, supposing to belong to the Catholic Kings, Isabel and Fernando, timed thus at least 15th century is the called ‘yugo y flechas’, which appears later even among Bankers Rothschild ‘properties’ and as symbol of the arising extreme right movement ‘Falanges’.
cut Spanish flag with the ‘yugo y flechas’ to the right
London Rothschild Bank logo with same symbol
Flag of the extreme right movement Falanges de las JONS
more or less ancient symbols: http://www.galeon.com/escudoespana/simbolos.htm