Cheers mate, welcome to the forums! :]
I have no modding experience at all regarding the Silent Hunter series, but as far as I remember, all the map icons are TGA files, right? To my knowledge, there is no mod that completely removes the icons, but by editing the appropriate TGA file for your sub's symbol and editing the alpha channel, it should at least be possible to create a kind of "dirty fix". So the icon would be there, but not visible because the alpha channel renders the whole symbol to be transparent.
However this would probably lead to problems when plotting a course, simply because the game itself always knows your position and even if you don't see the symbol, the plot always begins at the position of your boat...
Apart from that, that's indeed an interesting thought, having to keep track of your own position...