Stick something like this in your .bashrc file:

# display red exit value if it isn't zero
PROMPT_COMMAND='EXITVAL=$?; '$PROMPT_COMMAND
GET_EXITVAL='$(if [[ $EXITVAL != 0 ]]; then echo -n "\[\e[37;41;01m\] $EXITVAL \[\e[0m\] "; fi)'
export PS1="$GET_EXITVAL$PS1"

Command exit values other than zero are displayed in the subsequent prompt:

Check out the little red '1'

(see the little red ‘1’).

It’s the

${?#0}

bit which includes the last command exit value in the prompt, unless the value is zero, in which case nothing is displayed.