Hip hop legend Jay Z could be set to release a new album, exciting fans who have been starved of his music for four years.

Huge billboard adverts around the US and UK have led to speculation that the 99 Problems rapper has secretly recorded his 13th studio album. Passengers on the New York subway and tube stations on the London Underground, such as Canary Wharf, have noticed sprawling billboards with the phrase "4:44" written in black font set against a plain peach backdrop.

Unusually, the 4:44 adverts seen around the borders of various music-related publications do not link to another website, leaving the mystery wide open.

However, tech-savvy fans have investigated the source coding for the adverts and found several references to Jay Z's music streaming service Tidal, such as "tidal-444", suggesting the album will receive an exclusive release on the platform. Another clue is that the adverts on the NYC subway were seen at Jay Street-MetroTech Station, a cryptic reference to the rapper's stage name.

Clues also lie in the phrase itself, 4:44. Jay Z and his wife Beyonce famously have a strong connection with the number four – the couple married on 4 April 2008 and have the Roman numeral IV tattooed on their ring fingers; both were born on the fourth day of a month (September and December, the 8th and 12th months of the year), their five-year-old daughter Blue Ivy is said to be named after the Roman numeral for 4 (IV), Beyonce titled her fourth studio album 4 and Jay Z is the owner of sports bar 40/40. Also, it has been four years since the release of his most recent album.

Aside from a handful of guest spots, Jay Z, 47, has been largely absent from music in recent years. His last album, Magna Carta Holy Grail, was released in 2013 and the rapper has not mentioned any solo music since. Hip hop producer Swizz Beatz fuelled rumours that Jay Z was returning to the game in May, when he posted a photo of the pair together with the caption: "They don't even know what's about to happen... Album ModeZone."

4:44 is coming.. - #JayZ is that you? - #SippAndListen #RocNation #444

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Angel numbers in the subway?! Well OK then Brooklyn! 😄👼🏼 #angelnumbers #444 #positiveenergy #manifestation #JayStMetrotech #NYC #subway

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#444 #ComingSoon #StayTuned #HOVA #Repost @saintcharles ・・・ ALL IS WELL #444

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If the album rumours are true, it appears Jay Z is preparing to release new music ahead of his festival performances this summer. The rap mogul is scheduled to headline his own Made In America event in September and is also set to star at the UK's V Festival in August alongside Pink.

The Empire State Of Mind hitmaker certainly has his hands full at the moment with Beyonce, 35, expected to give birth to twins any day now.

Jay Z Tidal
Jay Z is set to perform at Made In America and V Festival this summer Theo Wargo/Getty Images for TIDAL