If it doesn't print anything, it might be that the referred font (^AN) doesn't have the warning symbol. You need to find a font that has the warning symbol defined and install that font onto the printer.

^FX Draws a /!\ symbol via diagonal lines and boxes.
^XA
^LL400
^PW650

^FX Left side of triangle ^FS
^FO155,50
^GD150,300,10,,R^FS

^FX Right side of triangle ^FS
^FO305,50
^GD150,300,10,,L^FS

^FX Bottom of triangle ^FS
^FO160,340
^GB300,10,10

^FX top of exclamation point ^FS
^FO295,110
^GB30,160,20

^FX dot at bottom of exclamation point ^FS
^FO295,290
^GB30,30,20,B,8
^XZ
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go to http://xmodem.net/warning.jpg in your browser to see the image or just copy my code and print it then "fiddle".

or view the code's label on screen: use http://labelary.com/viewer.html