I've used both Micoscale decal stipes and WS dry transfers. The problem with decals is that they are difficult to handle and the yellow tends to fade out against a concrete color surface. The dry transfer colors look better but they are really only good on a smooth surface. Any irregularities and the dry transfers won't adhere properly. I tried them on my brick streets and it was a disaster. Both decals and dry transfers need to be sealed with something like Dullcote to make them permanent or they will start peeling or breaking off.
I've also used a fine point paint marker and a straight edge with success...as long as the line was straight. Doing curves is a pain to get right. I've used crepe paper tape to form the curves and then painted inside the mask but I finally thought, as long as I'm already using tape, why not get tape that works as a line. Thus, I now use drafting tape. It's flexible and can be pulled into most curves by eye. It doesn't need any sealer and sticks so well that it will pull up any paint on the surface if you remove it.