[carlmr]

I always just imagined that it was signs that tell a tale. And the online etymology dictionary seems to confirm that.

https://www.etymonline.com/word/telltale

>also tell-tale, "discloser of secrets," 1540s, from tell (v.) + tale. As an adjective from 1590s. Phrase tell a tale "relate a false or exaggerated story" is from late 13c.

Is it maybe that the nautical term comes from plain English?

[Digit-Al]

Quite a lot of folk etymology tries to, incorrectly, assign nautical origins to common words and phrases. I used to read a column by an etymologist that jokingly referred to this using the term CANOE - the Committee to Assign a Nautical Origin to Everything :-)