I've tracked down the GM's email address and sent an email a month or so before my arrival date. My typical email will look something like this:
Dear [GM's NAME]
My wife and I have a reservation to stay at your hotel for X nights from [DATE]. I just wanted to drop you a line to tell you how much we are looking forward to our stay. This will be our first trip to [DESTINATION] and a celebration of [OCCASION] and we absolutely cannot wait. Though we considered many other properties, we have heard such good things about the [HOTEL NAME] from multiple friends and acquaintances that choosing to stay with you was an easy decision.
Thank you very much. We are truly looking forward to spending [OCCASION] with you.
Sincerely,
Obviously, I adjust that middle section about it being our first trip to say something else if it is not actually our first trip. If you've stayed at the hotel before, you could add something about how you had such a great time when you've stayed in the past.
As you can see, I ask for nothing explicitly and, sometimes, I get nothing. But most of the time, the hotel will do something to recognize your special occasion. A follow up phone call the week before arriving is probably a good idea as well, though I have not done this myself.
-S