I've signed a matte graphite blank with Testers Silver Metallic and a caligraphy pen. Came out really nice.
Does this need a coat of epoxy over it, or will the Testers last?
I'd rather not have this portion be glossy, but can live with it if necessary.

I use a wipe on poly...its what I use and it works well.

I would coat it, let it dry/cure, then mask off the blank on either side of the inscription and scuff the gloss lightly with scotchbrite (or similar). Proceed with caution, you just want to knock the shine off.

coat it and mask off then hit with a quick spray of dull laquer. I do this for top coats when I paint and it dulls it all the way down. Testors top coat dull is the best i found

I just finished several tests with different options and found that if I scuff the blank lightly with a scotch-brite extra fine pad before I write on it and the use the wipe-on poly over top of the Testers' enamel, I got the results I was wanting. You are right that the epoxy look is too glossy and thick. The wipe-on poly I use is the clear satin. Hope this helps.