Thanks all - as some hsve said, well worth doing.
The lettering on the tyres is because I loved Customcar magazine in the 70s and 80s - all tyres lettered then and I still love it!
The lettering pen was bought from a motorcycle shop many years ago - I lettered all my bike tyres. It has a ball bearing inside which mixes paint when tube shaken and it must be good quality as its still working. The point retracts as pressure is applied to pump paint to point.
Company name/logo is Polco - tyre paint Lettering Pen 10ml
Have fun!