@COMMA[n] : Returns the number with the thousands separator inserted where appropriate.
Note: Some variable functions can directly generate a numeric result with appropriate thousand separators if you add a c to their scale parameter.
Examples:
echo %@comma[12345678]
12,345,678
echo %@comma[0.12345678]
0.12345678
echo %@comma[%_xpixels]
1,920
See also: @CONVERT, @FORMAT, @FORMATN.