I wanted to put keyholes on the back of some signs for easy hanging and thought I'd just do them on the router table because it would be quick and easy.
Quite frankly when I tried a sample piece I didn't feel comfortable trying the get the wood into the correct position, drop it down onto the spinning bit, and move it along the fence to right spot. Rule one: if you don't feel safe doing it — DON"T DO IT.
So next I thought about some exotic jigs but fell back on my old adage: Simpler is always better. (Good old Occam and his Razor.) So, I used a 5/8" straight bit to cut a through slot in some 1/4" mdf. Yes, I did it by dropping the stock onto the bit in the router table but I started with an oversize piece of mdf, the router bit wasn't very high, and I could see where it was while I was routing.
Then I trimmed the jig to 4" x 4" with the slot positioned so when the top edge of the jig was aligned with the top of the sign, the keyhole is in the right position. Then it was just a matter of drawing a keyhole center line on the sign, attaching the jig with double-sided tape, and plunge routing using a 5/8" guide bushing.
I was able to knock out six keyholes in record time - safely - with this simple jig.