To prevent errors: it is a kind of paint pen, similar to an EDDING, which is used to paint silicone joints white again. The advantage is, the varnish is extremely thin, so I flood the numbers grooves with it (by toothpick, where I have taken some of the paint out of that pen already before) When it is dried, I then remove the excess paint on the surface, around the numbers, with a credit card (scrape it off).
Advantage is, it flows well and evenly into the groove and can be used - hopefully - without clear coat.