Error symbols not showing in vim-syntastic

I am trying to add custom error symbols to syntastic in my .vimrc file as so:

" Error symbols
let g:syntastic_error_symbol = "✗"
let g:syntastic_warning_symbol ="∙∙"

But I think I have managed to break something. Now not even the default symbols are loading properly but I instead get S> instead of >> on the left-hand-side margin.

So not only cannot I not get my custom symbols, neither can I get the default ones. What happened?

The full syntastic settings are:

" ============== syntastic settings ===============
set statusline+=%#warningmsg#
set statusline+=%{SyntasticStatuslineFlag()}
set statusline+=%*

let g:syntastic_always_populate_loc_list = 1
let g:syntastic_auto_loc_list = 1
let g:syntastic_check_on_open = 1
let g:syntastic_check_on_wq = 0

" Specific checkers for tex
let g:syntastic_tex_checkers = ['chktex', 'proselint']

" Others
let g:syntastic_aggregate_errors = 1
let g:syntastic_enable_signs = 1

" Error symbols
" let g:syntastic_error_symbol = "✗"
" let g:syntastic_warning_symbol ="∙∙"

This works:

" Error symbols 
let g:syntastic_error_symbol = "✗"
let syntastic_style_error_symbol = "✗"
let g:syntastic_warning_symbol = "∙∙"
let syntastic_style_warning_symbol = "∙∙"