Tyre wear indicator ?

I seem to remember, from (quite) a few years back, there was a product sold to show up abnormal wear on tyres before you got to the "Oh s***, they're worn out!" stage.

Iirc it was a sort of paint, applied in a band across the tyres which, after driving a bit, showed how the wear was diistributed across the tread.

Does this still exist ?
And is/was it useful ?