@JanisTX - as
@jeanwilson &
@AnasaziWrites noted, lines can be "etched" onto paper/card stock using a blunt stylus and a straightedge. Instead of marking a line with a pencil and then erasing, you make an impression in the paper using pressure. AnasaziWrites makes a good point about a bone folder being too blunt and a compass being too sharp. I use an un-inked, closed ruling pen or the back of a butter knife or a ball point pen that is completely out of ink.
You'll be able to see the line in raking light, but it's rather inconspicuous. It will, however, always be there - you can't erase it. As
@InkyFingers says, the other downside is that sometimes pointed flex nibs catch on the divot and cause splatters. And as AnasaziWrites notes - some inks can bleed into the divot too.
Historically, medieval scribes used a blunt stylus (and quite a bit of force) to inscribe these lines in parchment so as to rule both sides at once. Ingenious! But note - the broad edge script floats
between the lines, not touching them.
I'll add that if you're going to photo/scan a piece, you can use a light blue (non-copy) pencil, like manga/comics artists use to do underdrawings, because they won't show up in digital reproductions. InkyFingers - you can try waiting overnight before you erase, but smudging is sort of a problem with certain inks (McCafferey's gloss black, I'm looking at you).
Best wishes on those place cards, Janis!
--yours, K