Remove the numerals (23456789) from the character set of Open Location Codes, yielding the 12 letters CFGHJMPQRVWX, a collection of letters designed so that it is difficult to spell profanities. (Difficult but not impossible: XXX, MF, CP, MJ.)
Not sure what it would be useful for.
As base 12, it's not much more information dense than plain base 10 numbers, which also can't spell profanities. (Though maybe they can: 666, 1488, 420, etc.)
Maybe use letters as a prefix code to indicate what the subsequent numbers mean. We get an additional "character", a separator, at the transition point from letters to numbers. Of course, we could also explicitly use a separator character.
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