Watermelons ?

They LOOK like watermelons, but as we are in San Francisco, the setting for Philip Kaufman's 1978 remake of "Invasion of the Body Snatchers", it's probably best to approach this situation with caution (they do look more like the "pods" in the 1956 version, I know). Anyway, I found these, unattended, in a rather deserted, not-very-scenic part of The City. I doubt they were grown on the spot.
I'm somewhat wary of buying produce from itinerant peddlers in industrial districts by freeways, so I walked on. You're next!