Dog tag markings?

[mannerheim]

Hi! does anyone knows what the german dog tag markings means?
3. J. E. B 328 and below 526 O <- is that O a blood group ?


gimme some facts or wild guesses.... thank you.

[Battlerelic]

3./Infanterie Ersatz Batallion 328, personal number 526 and the "O" stands for blood type as you guessed