You mean Red Cross? Red Star?

Iranian Red Crescent: Flood-Hit Iran Getting No Financial Aid From Abroad Due to US Sanctions

Red Commie? Red Buddha? Red Hindu? Red Mormons? Red Atheists?

Take a cue from grammar school, call it Red X. Or use this:

 But this is difficult to spot on the battle field relative to the simple 'plus sign' in red.

History:

On 17 February 1863, a five-member committee, the future International Committee of the Red Cross (ICRC), met to study Dunant’s proposals.

One of its main objectives was to adopt a single distinctive symbol backed by the law to indicate respect for army medical s ervices, volunteers with first aid societies and the victims of armed conflicts.
The symbol needed to be simple, identifiable from a distance, known to everyone and identical for friend and foe. The emblem had to be the same for everyone and universally recognizable.
On 26 October 1863, the first International Conference was convened. It included delegates from 14 governments.
In addition to adopting ten resolutions, which provided for the establishment of relief societies for wounded soldiers - the future Red Cross and, later, Red Crescent Societies - it also adopted the red cross on a white background as the uniform distinctive emblem.

So, look at the Red Cross. Think, what is a more simple, easily recognizable, symbol in the battle field? 

Israel screwed this up, they had to have a different symbol for themselves and started the mess.

Maybe Israel has a rule about arithmetic, Jewish kids have to use a different symbol to add?