Better alternatives:
Base64 without padding: compact.
Grouped decimals: slightly less compact than hexadecimal, but extremely easy to type and pronounce. E.g. 577-467-341-467
Same thing when speaking it out loud. 'B four D capital Q B capital F s thirty-one' is way more convoluted and error-prone than 'B four D Q B F S thirty-one'.
The best thing I've found that fits this criterion is Crockford's Base 32 [1], basically the extension of hex digits, removing letters ILOU.
But Base 32 (case-insensitivity by proxy) constrains us to 5 bits, which is only a 20% reduction over the 4 bits of base 16. So instead of the 20 bits `1ab2f` we could express them with something like `1qm3`.
Or we could be using words...
I suppose, though, there's an attraction in using b32 rather than b29... (Though I notice mid-word apostrophes are double-tap-selectable at least on macOS, so perhaps swapping 'a' for ''' would be advantageous, if more complicated to explain.)
Regardless of variance, I don't think I'd regard either the above or the name of a fat character in Austin Powers as "tamest of the lot".
Unfortunately, most of the references around the web link to Tirosh's original work on the WayBack machine, which used to be hosted on "tothink.com", but the new owners put a "robots.txt" which make even the old version unaccessible on archive.org
In general, pure-number systems are better if possible, but where you have issues squashing in enough data in suitably compact form, transitioning to alphanumeric is better.
You can also consider the use prefix-based systems, either utilizing temporal epochs or node-specific prefixes, both of which can utilize readable aliases.
Finally, for anything expecting human transcription, checksum systems are awesome!
git license-plate?