I also had never heard of any such origins.
The patent and trademark office has no record of any trademark for the word 'hemi' relating to cars. The first one to use those 4 letters was in 1974 for furniture casters; #73013709. It has long been a dead trademark.
I believe stripes would be considered as a design patent which are difficult to find, not a trademark.
The hemispherical head design was revived in 1964. These were the first engines officially designated Hemi, a name Chrysler had trademarked. Chrysler Hemi engines of this generation displaced 426 cu in (7.0 L). Just 11,000 Hemi engines were ultimately produced for consumer sale due to their relatively high cost and the sheer size of the engine bay required to fit it in. The 426 Hemi was nicknamed the "elephant engine" at the time, a reference to its high power, heavy weight and large physical dimensions. Its 10.72 in (272.3 mm) deck height and 4.80 in (121.9 mm) bore spacing made it the biggest engine in racing at the time.
you may have to dig deeper indoor search for trademarks many are auto only trademarks. As with he ford mustang they were actually taken to court because of the MUSTANG bicycle and the MUSTANG radio in use at that time. The court ruler that different lines of products did not at that time violate trademark laws.
found this in a mopar owners manual:
Automobility Program, Chrysler 200, Chrysler 200S, Chrysler 300C, Chrysler 300S, Glacier, HEMI, Imperial, Imported From Detroit, Mopar Vehicle Protection, ParkSense, ParkView, Pentastar, Sentry Key, SRT8, Stow 'n Go, Stow N Place, Tech Authority, Town & Country and Uconnect are registered trademarks and Chrysler 300C Platinum, Keyless Enter 'n Go, SafetyTec and Town & Country Limited Platinum are trademarks of FCA US LLC.