I say I'm delighted to see a post from you again, my Dear! I'd been wondering where you were; hope you had a good winter.

I think this phrase might have different significance depending on context. Here are some Google snippets for it:
Marking your Bingo Cards; you’ll indicate your choices by marking an X in the box next to the names of the candidates you want to vote for. A punch-card ballot; again marking the card if necessary while going up to the next fairway.

The first thing it makes me think of is that this particular mark (whatever it is) is but one of the many that will be required before a final goal can be achieved, such as a card that, when it proves that you got 10 haircuts at a place, will earn you a free haircut.