$NON-NLS x$ is specifically for externalization and internationalization. It marks a string as being inappropriate for externalization. Eclipse and potentially other IDEs can be configured to present warnings when strings are hardcoded into a program so that programmers remember to externalize. NLS stands for National Language Support.
The number after $NON-NLS- signifies which string on the tagged line the tag is for. The number 1 works for you, likely because there is only 1 string on the line your are trying to tag.
If you had 2 strings on the same line, you can, for example, tag only the second string using $NON-NLS-2$.
//Warning on "baz"
//Warning on "bar"
foo("bar","baz"); //$NON-NLS-1$ //$NON-NLS-2$
//Warning on "baz" (apparently the slashes are required even with multiple tags)
foo("bar","baz"); //$NON-NLS-1$ $NON-NLS-2$