Paint Marker Pens
The Slanchogled Sofia, Varna and online art stores offer Posca permanent acrylic opaque marker pens.
Suitable for nearly all surfaces including paper, wood, card, glass, ceramics and porcelain, stones and textiles they are popular for decorating surfs and skateboards, drawing on shirts, decorating windows or shop fronts and nearly everything else. You can follow the Posca website for more ideas and for step by step instructions.
The Posca PC-1M series is often called a nail fineliner or a Nail Art Pen.