A Norwegian expert on runes thinks he has finally cracked the code inscribed on a 900-year-old piece of bone. And what it says may be the Viking equivalent of a Valentine’s Day card.

K Jonas Nordby, a runologist at the University of Oslo, says after intense study of similar pieces of code, he believes the message scrawled into the bone reads simply: “Kiss me.”

Nordby has been studying runes for years, which were used in Germanic language alphabets before the adoption of the Latin alphabet. He’s been fascinated by the codes used by medieval Scandinavians -- particularly the jötunvillur code, which dates back to at least the 12th century and has eluded scholars for years.

Nordby thinks he may have made a breakthrough in the code after finally making sense of the “Kiss me” inscription on a piece of bone in Sigtuna, Sweden.

He tells The Guardian newspaper that the names of two men appear on the bone in standard runes. Then, after each name, is a combination of runes that appear to make no sense.

All runes have names, and Nordby finally realized that the code works by exchanging the rune sign with the last sound in the rune’s name. So, for example, the rune for the letter U is called “urr,” so it was encoded with the rune for ‘r.’

The only difficulty with the code is that many runes end in the same sound, he told Daily Mail Online.

“The problem with this code system is that it is impossible to read because the code gives many possible solutions,” Nordby said.

“It is, however, possible - with some uncertainty - to interpret the runic inscription on a piece of bone found in Sigtuna as ‘Kiss me’.”

That’s because the bone uses numbers in place of runes, making interpretation a little simpler.

Nordby thinks the code wasn’t used to convey secret messages, as many scholars have assumed, but in the teaching of rune code-breaking instead. He says that many who wrote coded runes also left comments in standard runes that urged readers to figure them out.

One inscription from the Orkneys, reads: "These runes are written by the most skilled rune writer west of the sea." Others urge the reader to "interpret this if you can.”

“People challenged one another with codes. It was a kind of competition in the art of rune making. This testifies to a playfulness with writing that we don’t see today,’ he told Mail Online.