Marker to write underwater

[Elvandar]

Hi, in the cave lake where we dive regularly, there are some sign to guide among the submerged "Attaction", cars, motorboat, ecc... like these:

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But there are some of them that are not readable anymore, because they faded after years underwater.

The faster way to make them readable is to change them, but out of curiosity, i searched online for a solution to write underwater, and i found these markers:
Sakura Solid Marker Original - Suitup - Art Supplies (suitupshop.it)

Do anyone have ever tried them or similar product? Except from the trusty pencil, did you use anything else?
I bought them anyway, if they are not usable for the underwater writing, I will still use them to decorate my white fins 😁

Edited September 14 by Elvandar

[Davide DB]

I didn't even suspect its existence.
Try them and tell us if they work!