From the longer Wikipedia article  - which contains images of the cryptogram and alphabet.
Olivier Levasseur (1688 or 1690 – 7 July 1730), was a pirate, nicknamed La Buse or La Bouche (The Buzzard) in his early days, called thus because of the speed and ruthlessness with which he always attacked his enemies.
Legend tells that when he stood on the scaffold he had a necklace around his neck, containing a cryptogram of 17 lines, and threw this in the crowd while exclaiming: "Find my treasure, ye who may understand it!" What became of this necklace is unknown to this day. Many treasure hunters have since searched for his fabulous treasure.
In 1923 the widow of a certain Charles Savy named Rose found some carvings in the rocks at Bel Ombre beach near Beau Vallon on the island of Mahé, due to the low water level that year. She found carvings of a dog, snake, turtle, horse, fly, two joined hearts, a keyhole, a staring eye, a ballot box, a figure of a young woman's body, and the head of a man. A public notary in Victoria heard of this news, and understood those symbols must have been made by pirates. He searched in his archives, and found two possible connections. The first was a map of the Bel Ombre beach, published in Lissabon in 1735. It stated: "owner of the land... la Buse" (Levasseur).
The second discovery was the last will from the pirate Bernardin Nageon de L'Estang, nicknamed le Butin , who died 70 years after Levasseur, and claimed to have obtained possession of some of Levasseur's treasure. It contained 3 cryptograms and 2 letters, one to his nephew:
"I've lost a lot of documents during shipwreck.. I've already collected several treasures; but there are still four left. You will find them with the key to the combinations and the other papers."
and one to his brother:
"[..] Our captain got injured. He made sure I was a Freemason and then entrusted me with his papers and secrets before he died. Promise your oldest son will look for the treasure and fulfill my dream of rebuilding our house. [..] The commander will hand over the documents, there are three."
The notary contacted Mrs. Savy, and after some excavations at the 'staring eye' they discovered two coffins containing the remains of two people, identified as pirates by the gold rings in their left ears, as well as a third body without a coffin, but no treasure was found at this location.
In 1947 Englishman Reginald Cruise-Wilkins, a neighbour of Mrs. Savy, studied the documents, but the cryptogram was much more difficult to solve than first believed. Deciphering it could be carried out only by starting from the two letters and the three cryptograms compiled in mysterious alphabet, a rebus, or at least in initiatory writing which could be put in relation to masonic symbolism. Cruise-Wilkins then discovered a connection with the Zodiac, the Clavicles of Solomon, and the Twelve Labours of Hercules. Various tasks, representing the Labours of Hercules, had to be undertaken in strict order. The treasure chamber is somewhere underground and must be approached carefully, to avoid being flooded. It is protected by the tides, which requires damming to hold them back, and is to be approached from the north.
Until his death at Réunion, Cruise-Wilkins sought and dug in the island of Mahé. In a cave, except for old guns, some coins, and pirate sarcophagi, he did not find anything. He died on 3 May 1977 before he broke the last piece of code. His son, Seychellois history teacher John is currently still seeking for the treasure, concluding that after using state-of-the-art equipment, he needs "to go back to the old method, [getting] into this guy's mind, [claiming he is] ten down, two to go in his Herculean Labours.
An article on John Cruise-Wilkins activities here .