Vim: Show the index of tabs in the tabline

put this in your vimrc

" Rename tabs to show tab number.
" (Based on http://stackoverflow.com/questions/5927952/whats-implementation-of-vims-default-tabline-function)
if exists("+showtabline")
    function! MyTabLine()
        let s = ''
        let wn = ''
        let t = tabpagenr()
        let i = 1
        while i <= tabpagenr('$')
            let buflist = tabpagebuflist(i)
            let winnr = tabpagewinnr(i)
            let s .= '%' . i . 'T'
            let s .= (i == t ? '%1*' : '%2*')
            let s .= ' '
            let wn = tabpagewinnr(i,'$')

            let s .= '%#TabNum#'
            let s .= i
            " let s .= '%*'
            let s .= (i == t ? '%#TabLineSel#' : '%#TabLine#')
            let bufnr = buflist[winnr - 1]
            let file = bufname(bufnr)
            let buftype = getbufvar(bufnr, 'buftype')
            if buftype == 'nofile'
                if file =~ '\/.'
                    let file = substitute(file, '.*\/\ze.', '', '')
                endif
            else
                let file = fnamemodify(file, ':p:t')
            endif
            if file == ''
                let file = '[No Name]'
            endif
            let s .= ' ' . file . ' '
            let i = i + 1
        endwhile
        let s .= '%T%#TabLineFill#%='
        let s .= (tabpagenr('$') > 1 ? '%999XX' : 'X')
        return s
    endfunction
    set stal=2
    set tabline=%!MyTabLine()
    set showtabline=1
    highlight link TabNum Special
endif

On the wikia page you may find at least two (the ones I tested) which give you the tab indices, and one of them produces the number of windows inside each buffer which have edits.

Here is the result of my modifications on the one that produces the count of edited buffers, the change I made was to make the highlight value of the count consistent with the rest of the tab:

set tabline=%!MyTabLine()  " custom tab pages line
function MyTabLine()
        let s = '' " complete tabline goes here
        " loop through each tab page
        for t in range(tabpagenr('$'))
                " set highlight
                if t + 1 == tabpagenr()
                        let s .= '%#TabLineSel#'
                else
                        let s .= '%#TabLine#'
                endif
                " set the tab page number (for mouse clicks)
                let s .= '%' . (t + 1) . 'T'
                let s .= ' '
                " set page number string
                let s .= t + 1 . ' '
                " get buffer names and statuses
                let n = ''      "temp string for buffer names while we loop and check buftype
                let m = 0       " &modified counter
                let bc = len(tabpagebuflist(t + 1))     "counter to avoid last ' '
                " loop through each buffer in a tab
                for b in tabpagebuflist(t + 1)
                        " buffer types: quickfix gets a [Q], help gets [H]{base fname}
                        " others get 1dir/2dir/3dir/fname shortened to 1/2/3/fname
                        if getbufvar( b, "&buftype" ) == 'help'
                                let n .= '[H]' . fnamemodify( bufname(b), ':t:s/.txt$//' )
                        elseif getbufvar( b, "&buftype" ) == 'quickfix'
                                let n .= '[Q]'
                        else
                                let n .= pathshorten(bufname(b))
                        endif
                        " check and ++ tab's &modified count
                        if getbufvar( b, "&modified" )
                                let m += 1
                        endif
                        " no final ' ' added...formatting looks better done later
                        if bc > 1
                                let n .= ' '
                        endif
                        let bc -= 1
                endfor
                " add modified label [n+] where n pages in tab are modified
                if m > 0
                        let s .= '[' . m . '+]'
                endif
                " select the highlighting for the buffer names
                " my default highlighting only underlines the active tab
                " buffer names.
                if t + 1 == tabpagenr()
                        let s .= '%#TabLineSel#'
                else
                        let s .= '%#TabLine#'
                endif
                " add buffer names
                if n == ''
                        let s.= '[New]'
                else
                        let s .= n
                endif
                " switch to no underlining and add final space to buffer list
                let s .= ' '
        endfor
        " after the last tab fill with TabLineFill and reset tab page nr
        let s .= '%#TabLineFill#%T'
        " right-align the label to close the current tab page
        if tabpagenr('$') > 1
                let s .= '%=%#TabLineFill#%999Xclose'
        endif
        return s
endfunction

The tabline plugin is a vim plugin that implements requested functionality and won't blow out your vimrc. Simply install, and restart vim.

To install:

cd /usr/share/vim/vimfiles/plugin/
wget https://raw.githubusercontent.com/mkitt/tabline.vim/master/plugin/tabline.vim

or use a plugin manager.