If TortoiseSVN icons are not visible in the File Explorer, it could be that you are running a 64-bit version of Windows with 64-bit version of TortoiseSVN installed.
On computers running 64-bit version of Windows, both 32-bit and 64-bit versions of TortoiseSVN must be installed in order to be able to see TortoiseSVN icons in the File Explorer panel. They are compatible and can be installed both at the same time.