I make out the hallmark to be "GBR JSRAEL 1916," for Gebruder Israel. The helmet is the M1915 for Jäger zu Pferde, which Israel did manufacture.
In German, the interchangeability of "J" and "I" originates with the 23 letter classical Latin alphabet, for which no distinct consonant "J" existed until medieval times. The same is true for the letter "U," which, originally, was a altered form of the letter "V."
This is why one encounters "Iohannes Wagner" on Iron Crosses made by Johannes Wagner, "Jsrael" for Israel, and "Gvstaf" for Gustaf. The alphabet was based on the sounds of letters (in this case vowels) not their shape.
I think the helmet is good, albeit battered.