The German 88mm gun was famous and feared for its accuracy and penetration over long distances during WW2. It was used in anti-tank roles and mounted on armored vehicles but was originally designed for another purpose. What was it originally designed to do? Also how did German gun crews "mark" and take credit for their kills?

It was originally designed as an anti-aircraft weapon

You got it sailracer, I added a tidbit right after I posted but you beat me to it, can you answer part 2?