I found an article on the history of cryptarithms [link] that gives an example that is possibly the earliest published example of the genre (although the term cryptarithm had yet to be coined).
In American Agriculturalist, December 1864, the following puzzle was posed in the “Boys & Girl’s Column”:
From American Agriculturalist, December 1864 [link]
No. 109. — Mathematical Puzzle
The ten letters represent the ten Arabic digits, 1, 2, 3, 4, etc. What value will you give to each letter so that this example of multiplication will be correct — each letter always having the same value.
If the mathematicians of the Agriculturist family fail to solve this by calculation alone, a clue may be given to another method of finding the answer.
In the January 1865 issue the following was published:
No. 109. — Mathematical Puzzle. — As but few have answered this correctly, (their names are below), we give now only a clue which will make it easier, viz: the different letters employed in the problem, when properly arranged, give the name of a noted English statesman of the present day.
And the answer was given in the February 1865 issue.
(The relevant issues of American Agriculturalist can be viewed at the Internet Archive [link] (see page 349).
[AmAg109]