Hi Casey,
I'll tag onto the majority with this one. In my own experience, most people tend not to be very observant. There's an experiment which involves showing people a video of a sports match and in the middle of the video, a man in a gorilla suit runs accross the pitch, stops in the centre of the screen and waves to the camera, then carries on running. He's right in the middle of the screen, but something like half of the people who watch the video, do not notice the guy.
The late Terry Pratchett was right when he joked that the great percentage of the brain that no one knows the purpose of, is actually very busy, stopping people from noticing the things which would freak them out if they ever did notice them.
I'm a picker rather than a cutter, but I often have deep cuts visible on my hands and arms, that I get from a variety of external causes. I've currently got a big red one half way up the inside of my left fore arm, that looks like it could be SH, but isn't.
I think I've only been asked about cuts once, and I was able to honestly answer that I got them playing with an animal I'd adopted. The person who asked was a surgeon who was about to straighten my nose in the hope that I could breathe through it again. he never asked how my nose got broken and twisted...
It's an interesting challenge that you are posing for yourself. Please let us know how it goes, especially in the culture that you are living in. I don't know if it is still the case, but all of the former eastern bloc countries used to have hideously high suicide (completion) rates, and I would be surprised if that wasn't accompanied by an even higher frequency of other self harming behaviours.
now to see if I can leave my upper arms alone for long enough to wear very short sleeves this summer...