The free Fix File Encoding extension prevents Visual Studio 2017/2015/2013/2012 from adding BOM to UTF-8 files.

Normally, when you edit a UTF-8 file in Visual Studio, it adds the byte order mark (BOM) sequence 0xEF, 0xBB, 0xBF to the beginning of the file. Sometimes it confuses other applications further processing the file. You can select an encoding manually (File - Advanced Save Options... or File - Save As... - Save with Encoding...), but you need to do it each time you reopen the file.