Hello mate, nice find. It does tell a lot of stories. This helmet was used by at least two different soldiers, as I can make out two different names and two different locations (probably of the home garrisons). One I can make out clearly (on the 2nd pic from bottom - righthand side of your finger) is "е-р Христов - e-r Hristov" (Efreitor Hristov - Private first class Hristov). Next to his name is the garrison town name, abbreviated as Mih-Grad (Mihaylovgrad, now Montana). Next to it you can see a roman 1 (I) + R (bulg.: P) and "Ohrid", this is the units abbreviation 1st Platoon named after Ohrid (btw. a Lake and town in now Macedonia - also well known for a battle of ancient Bulgarian times). In front of the abovementioned name Hristov is another name, but I can't really make it out.
On the 1st pic from bottom, the 59 is the head size, next to it the text which is clearly visible is another garrison town abbreviation D-Grad (Dimitrovgrad), wht is written below that, I can't make out, sorry. And then you can see МДБ (MDB) and БИК (BIK). MDB is the abbreviation for "Механизирана Димитровградска Бригада" - Dimitrovgrad Mechanized Brigade, now (as of 1992) officially known as the "61-ва Стрямска механизирана бригада" - 61st "Stryamska" Mechanized Brigade, Garrison HQ in Karlovo. As for БИК (BIK) I have to guess, since this abbrevation has got several meanings in Bulgarian, one and the main meaning is "Bull", so it could well be the nickname of the helmets former wearer.