Reinforcing the point that "of" often doesn't make it into acronyms, USA omits the of. United States of America would look strange to most people as USoA. If absolutely necessary, I have very occasionally seen US of A. As opposed, I guess to the former Union of South Africa as U of SA. Its a Republic now, not a Union. More Union bashing.
There is a USO. United Service Organization. Entertains and provides services to the Army, Navy, Marines, Air Force and any and all other armed services. Mostly overseas. The Red Cross used to do some of that work, hence donut dollies, take two, no more. But they have cut back to mostly domestic civilian (disaster, etc.) work. There is a separate International Red Cross, to which the ARC belongs. I think the International includes red crescent for Moslem countries and whatever Israel uses, the hexagon symbol. It was based on the Swiss Flag, with colors reversed. Some places are more sensitive about crosses than others. Vampires?