The note was quite typical of the couple, Prince Albert and Princess Charlene. It was written on a pre-typed card with his monogram (Charlene has her own, and the couple also has a joint one). The signature is printed on. Per usual, with Monaco, the note was bilingual, written in both English and French.
The note was dated the 14th, which is Prince Albert's birthday. Pre-typed notes often have the date of the special occasion, or else the month the reply was written.
The letter is postmarked the 24th. The letter took 6 days to arrive in the mail, which is sooner than average for Monaco.
The card says:
Palace of Monaco14th March 2015
Touched by your kind thoughts for my birthday, please accept my most sincere thanks.
Albert de Monaco