They only mention code protection, which is usually an option you configure when you blow the firmware. There should be more info on this in the application data book/doc, because there is nothing else in the data sheet.
I repaired and programmed cash registers (Olivetti/Uniwell range) many moons ago and regularly wiped and reprogrammed eproms (the SGS Thomson 27C128s /256s) for these machines over a few years and recall the software program running on the terminal had a comprehensive menu.. Very possibly password protection was a feature on there. We never used it though. Get hold of any cash register repair business, their techs will advise if password protection is on there and if theres a way around it. These machines are still in use today, so you will have some luck. I think it may be a user-programmed password though. Try scratching around for some documentation from SGS Thomson, might just find something.
Keep that little glass window covered (with a label/sticker) Exposure to UV for long enough will erase the data on there if left uncovered.