| > People that rout signs often use either a "V" groove or core box bit. | | This is good advice, as over the weekend, I will try anew. | | I want whatever is easiest to control in very soft wood, so, I will | try the V-groove. |
It seems like you're making an awfully big job out of this. Controlling a router freehand to make letters is going to be nearly impossible. Even routing a straight line against a fence is tricky. The bit tends to wander and a wood with rough grain, like fir, will cause it to wobble. Using a dremel tool might be more realistic, but still not easy. Then once you've routed, then what? Are you going to squeegee white paint into the grooves? That's a tricky job, too, if you want it to look good.
Why not just use a permanent marking pen? If that doesn't look official enough for a school bathroom pass, you can get stick-on letters at Home Depot for about $3. If that seems not durable enough you could coat them with polyurethane or acrylic resin.
For any of those options you'll probably need to first paint the wood a light color. The piece you have looks like it's a scrap of pine stained with very dark "walnut" stain. Ugly. Hard to see. And requiring you to use light- color letters. On the other hand, why not just use a fresh piece of wood? You could get a pine 1x2 for a couple of dollars, stick on black letters, then polyurethane the whole thing. Then you'll have a nice looking pass that looks official, and the kids won't need two hands free to carry it.
All for less than $10 if you have polyurethane on hand.