My husband and I simply called RCCL and informed them it was our honeymoon. We married in Oct and cruised in Feb. RCCL never asked when we were married, so I doubt they would have any way to verify. They noted it on our reservation and we found an invitation to the event in our stateroom upon arrival. The event was a champagne breakfast in the main dining room. We received free mimosas, which were delicious, and 2 free chocolate covered strawberries. We were also seated at a nice table for two near the windows. The entire back corner of the main dining room was sectioned off for honeymooners, but the tables were for 2 only. There were plenty of couples there, but no one seemed to be socializing. Maybe it was too early and they had partied too much the previous night!
Anyway, if you call RCCL or your TA they should be able to note it for you and you should find your invite sometime during your cruise. I would suggest some other onboard activites for socializing, though. If you drink, any of the bars should do. The hottubs late at night were also hot spots.
Hope this helps, and enjoy your honeymoon!
Serenade OTS 10/2005
Freedom OTS 9/2007 and 4/2008
Majesty OTS 2/2009
Monarch OTS over and over and over again
Carnival Imagination 5/2009
Oasis OTS 2/2010
Grandeur OTS 3/2010