German 88mm flak gun model

Hello, do you know what the bottom symbol stands for on the peice of armour in this photo?

Thank you

http://www.flyingmule.com/img/prd/DM-60630_01_lrg.jpg

 

I was intrigued, so looked it up:

http://www.flyingmule.com/img/prd/DM-60630_01_lrg.jpg

The bottom appears to be a stylized bunker. So maybe that represents the fortification 'kill count'?

 

That's what I took it as, earthen bunker with firing slit. Pretty much self-explanatory.