If you're getting a PCB company to manufacture according to your Gerbers... When you place SS legends you can put them anywhere and any size or direction you choose, you can even have pictures and cartoons if you want!. Try and place SS legends outside any solder mask outlines, and outside from vias, PTH's and un-PTH's. They can go on top of tracks no problemo, but if you put then under a component geometry, remember that your legend will be covered up.
If you scew up and and place legends where they clash, it's not much of a problem, the PCB people will "clip" the silks to fix the problem.