Well, was interesting how easy it was to find a lot about this mark using online searches that lead to the primary sources from Russian Empire (unfortunately all in Russian). Turns out that was the mark of the Donetsko-Yuryevskoye Metalurgical Company, one of the notable steelmakers of the late Russian Empire. You can see more of their marks on rails in the Google image search. It was incorporated in 1895 (its incorporation papers can be found here), and owned several factories around the empire (see No. 11 on the right page here - link markup doesn't work; I guess Cyrillic letters are confusing Markdown?)

Here is a surprisingly well-sourced LiveJournal post about the company: Stamp on the rail. Donetsk-Yuryev Metallurgical Society

Given that this this railway cutout has the steelmaker's mark and not the railway's mark, it's difficult to determine which railway this was used for, since by 1903 (when this was presumably manufactured) Russian Empire already had several railways under construction in any given year.