What does the output from CTRL+N in Windows Command Prompt mean?

The ASCII standard has two code points, SHIFT OUT and SHIFT IN that switch between two different modes.

Historically, these were black and red typewriter ribbon. The instance you see is a VT100 compatible terminal emulator, which uses these to switch between regular text and line drawing characters. This is a simple data compression standard, in which bit 7 of each character is set from the current shift state rather than transferred, which gives a slight speed boost over a serial link.

It is a "not recognized as an internal or.... " message, but it seems that it isn't displaying correctly. Be sure that command prompt fonts are set to raster.

If I paste the output here, I get the same scrambled characters you do, presumably due to character encoding. Here's the cmd output as a screenshot:

It seems as if the symbol is a UTF-8 symbol, since N++ won't render it correctly in ANSI, but will in UTF-8

U+266B  ♫   e2 99 ab    BEAMED EIGHTH NOTES

http://www.utf8-chartable.de/unicode-utf8-table.pl?start=9728

You will notice that pressing Ctrl and other letters will produce other symbols, such as the spades symbol for Ctrl+E