The file must be named exactly guildmark.bmp (all lowercase). Note: For Union Emblems, the name must be unionmark.bmp .
The game will automatically search your local directory for the file with the specific name and apply it. Troubleshooting & Tips File Location: guild emblem silkroad 16x16 upd
If you downloaded a "16x16 upd" pack and it fails, check these issues: The file must be named exactly guildmark