The letters are not in a recess, and there is a dot (a full stop) after R&B. The incision "AI", which might not stem from the manufacturer, could in my view refer to an owner, although I have no idea who that is.
The knife has been wrung (twisted), and it was used as a tool by my late grandfather who lived in Central-Eastern Finland in the 20th century. The knife is certainly more than 50 years old. I have checked the Finnish, Swedish and Russian hallmarks to no avail. The German brand Robbe & Berking seems out of question here, since according to your site http://www.925-1000.com/Fgerman_marks_a1884_8.html they started using the abbreviation R&B in the 1960's.
Kalle
