When you install a new WordPress theme, check to see what it does for 404s and unfound search pages. You may be surprised at the message you’re giving your readers.
For example, the popular Cutline theme produces “Easy, tiger. This is a 404 page. You are totally in the wrong place. Do not pass GO; do not collect $200.” for 404s and “Welp, we couldn’t find that…try again?” for empty searches. These may or may not fit the impression you’re trying to convey.