What's similar?

[MochaDuck]

I guess, but that's not exactly what I had in mind.

What did you have in mind?

 

[MochaDuck]

I just thought if another. Smoke from fire was used for signals/codes, and letters are used to make codes too

 

[CarpCharacin]

What did you have in mind?

Letters can be typed on a keyboard, and some keyboards are made with ABS, which can contain bromine based fire retardants which photocatalytically degrades the plastic, and turns it yellow.

I just thought if another. Smoke from fire was used for signals/codes, and letters are used to make codes too

That one is good!