Pictured above is the current Spanish flag with the eagle removed from the coat of arms (1981)
The shield in the centre of the Spanish flag includes the Royal seal, which is flanked by two crowned pillars (the Pillars of Hercules) bearing the inscription 'Plus Ultra'.
According to Spanish legislation, the height of the coat of arms should measure two fifths of the flag's width (i.e. hoist), and should appear in the middle of the yellow stripe. The flag's usual proportions are a length measuring three halves its width, in which case the distance from the hoist of the shield's vertical axis should be half the flag's width. In other instances (should the flag be either shorter in length or square) the coat of arms should appear in the centre.
Flag mourning customs
In the UK to symbolise mourning, the Union Jack is flown at half-mast. In Spain they have their own system:
The most frequent alternative to flying a flag half-mast to indicate mourning is to stitch a small piece of black material to the centre of the flag. This is done almost only with flags not intended for hoisting, such as long flags displayed horizontally on balconies etc. Flags not intended for hoisting but which would be inappropriately defaced by such an addition (namely military colours) tend to use a black cravatte attached to the finial.