Cyrillic letter "ч." appears after clock on iOS 12

Solution 1:

I had the same problem and I did so : settings/language & region/iPhone Language/English(UK) My phone was already with this option but I chose it anyway and luckily the symbol get disappeared. I hope I helped. Good luck.

Solution 2:

I believe it is related to the device language settings. I just tried to change language of my iPhone to Bulgarian (I guess it is Bulgarian on your screenshot) and the Cyrillic "ч" appeared after the time. If you believe this is incorrect — drop Apple a feedback or bug report.