Display the status code of the last executed command. Add this snippet to your .bashrc or .zshrc file.

.bashrc

col_success="$(tput setaf 10)"
col_failure="$(tput setaf 9)"
col_normal="$(tput sgr0)"
col_fade="$(tput setaf 15)"

function _prompt_() {
    local code="$?"

    if [ "$code" -ne 0 ];
    then
        if [ "$code" -gt 128 -a "$code" -le 192 ]
        then # Failure or Signal
            echo -n "${col_fade}[${col_failure}${code}${col_normal}/${col_failure}"
            echo -n $(kill -l "${code}" | tr '[:upper:]' '[:lower:]')
            echo "${col_fade}]${col_normal}"
        else # Failure
            echo "${col_fade}[${col_failure}${code}${col_fade}]${col_normal}"
        fi
    else # No error
        echo "${col_fade}[${col_success}${code}${col_fade}]${col_normal}"
    fi
}

PROMPT_COMMAND="_prompt_"

.zshrc

col_success="$(tput setaf 10)"
col_failure="$(tput setaf 9)"
col_normal="$(tput sgr0)"
col_fade="$(tput setaf 15)"

function precmd() {
    local code="$?"

    if [ "$code" -ne 0 ];
    then
        if [ "$code" -gt 128 -a "$code" -le 192 ]
        then # Failure or Signal
            echo -n "${col_fade}[${col_failure}${code}${col_normal}/${col_failure}"
            echo -n $(kill -l "${code}" | tr '[:upper:]' '[:lower:]')
            echo "${col_fade}]${col_normal}"
        else # Failure
            echo "${col_fade}[${col_failure}${code}${col_fade}]${col_normal}"
        fi
    else # No error
        echo "${col_fade}[${col_success}${code}${col_fade}]${col_normal}"
    fi
}