Though Callahan's Diner was a set built for the film, the Callahan's Diner logo and window script is identical to that used by Callahan's Diner at 1213 Wilshire Boulevard in Santa Monica, California. It's quite likely that members of the cast and/or crew of the film were familiar with the Santa Monica restaurant and used it as an art model for the San Francisco locale. The "Dirty Harry" reference inherent in the Diner's name may simply be an added plus.
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