I put a few coats of Tru-Oil on the bow as normal. Where I'm writing, I spray with satin poly and let it dry then write with the India Ink. After it dries I add the rest of the Tru-Oil finish.
I tried that recently on a really fine mulberry flatbow. Two coats of Tru-Oil, signed with a pigmented ink that cannot fade. I gave it a light going over with 0000 steel wool and then 6 coats of spray on satin finish poly-you're-insane. Looked pretty darn good so I thought. So did the guy in Noatak, Alaska when it arrived. He loved it until he got down to the lower 48 and was shooting it in a higher humidity climate! The finish turned hazy, started to blister and peeled up in chips. Something was incompatible between those two finishes.
I've promised to fix it for him and this time it's nothing but a dozen handrubbed coats of Tru-oil and a final buff with ultrafine steel wool to dull the finish. Pity I can't find a pen that Tru-Oil doesn't wipe off!