The Burgundy Cross is a variation of the St. Andrew's Cross. The rough outline symbolizes the branches of the trees on which Saint Andrew was crucified. Andrew is the patron saint of Burgundy.
This cross was featured on the flag of Spain that was introduced by Philip I, Duke of Burgundy. Although Burgundy is a long way from Spain, in 1516 this cross was established as one of the country's banners by the Duke's son, Charles V, the first monarch of the House of Austria.1
Even further away from Burgundy, the design was brought to the state of Florida during the Spanish rule from 1565 to 1763. This is also known as Cross Ragulée or Ragged Cross. (See also The Old Rugged Cross.)
A different style cross was used for a war medal and called the Spanish Cross. This was issued by the German Army in World War II to soldiers who fought in the Spanish Civil War to support Francisco Franco's nationalist forces. This medal has the shape of the Maltese Cross with a Swastika in the centre. Although this medal was called the 'Spanish Cross', it was created by Germany, for Germans, and therefore cannot be said to represent Spain.
Different regions in Spain have crosses as part of their flags, for example Asturias and the Basque region. But if you are looking for a cross that represents Spain, the Burgundy Cross is probably the closest you can find.
In this regard, Spain differs from many other European countries, especially Nordic countries, which are identified with well established crosses. One possible reason is Spain's history of being an Islamic country from 711-1492. Where Northern European countries had a virtually uninterrupted Christian influence for over 1,600 years, Iberia's ancient Christian symbols were either destroyed or fell into disuse. Portugal similarly has no readily identifiable cross.