After being out for a couple of weeks, my first request to Meoli was sent back to me as 'return to sender,' which usually means I used an outdated or incorrect address - in some cases, an 'RTS' may mean my request was refused by the intended recipient, though that did not seem to be the case here.
I did some 'quick research' to find a presumably updated address and sent my request back into the wild - I finally got my card signed in about a week or so.