Original Glock 23 (40) rear sight marked "-" or not?

[perro loco]

I have a G23 serial EEK***
Rear sight have on side a minus "-" or line marked on it.
Is this a sign that I´m using a special sight or not?

Checked Arotek site and they have rears marcked as +0

"+0 Aro Site Rear Target Sight G-17, 19, 22, 23, 24, 34, 35, 37"

Is this a advice that i´m runing wrong sights or is only arotek´s own marks?


thanks folks, planing to get some new rear sight, loosed rear on range this weekend. Can´t remember marks on it, was Arotek too

cheers

PL