Ramstein is notorious for a very horrible acident.
During an airshow, 3 Italian jetplanes collided and 1 of them fell into the cheering crowd, killing 80 people and badly burning a few hundred.
That accident is important because after it a new air show standard was set, that prohibits the planes to perform too close to the crowd and no plane can at any time approach the crowd to avoid any further accidents.
The song Rammstein was a dedication to that event.
Since so many people liked the dedication, the band became known just by that song. They took the name and added the extra "M".