I've seen there are several issues on GitHub concerning square brackets around file/folder symbols in NERDTree (for instance this, which is on vim-devicons' repo, rather than NERDTree's)
None of them, however, seems to refer to square brackets around the read-only symbol
g:NERDTreeGlyphReadOnly, which is
RO by default. It is fine to have square brackets in this case, but if I use the lock devicon
"\ue0a2", then it's a bit ugly to retain the square brackets too.
g:NERDTreeGlyphReadOnly was introduced with this merge, and there I read this note from the author:
NOTE - I left the square brackets around the indicator so users don't have to deal with issues escaping characters.
So does this mean that there is no configuration that removes those square brackets?