5SOS who? Aussie rockers 5 Seconds Of Summer have application to trademark their nickname rejected

They're one of the hottest bands in the world and boast almost six million followers on Twitter.

But apparently 5 Seconds Of Summer aren't famous enough to be trademarked. 

The Australian group recently had an application to register their initials 5SOS rejected, reports the Herald Sun.

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Not well known enough: 5 Seconds Of Summer have reportedly had an attempt to trademark their nickname 5SOS rejected

Not well known enough: 5 Seconds Of Summer have reportedly had an attempt to trademark their nickname 5SOS rejected

An office delegate at Trademarks Australia told the publication at the weekend that the popular nickname synonymous with the rockers isn't 'notorious'.

'The name of this group is not notorious,' Iain Thompson said before admitting he personally didn't know who the pop band, who toured with One Direction, were.

Calum Hood, Ashton Irwin, Michael Clifford and Luke Hemmings became one of the most popular artists in the US last year after their self-titled debut album rocketed to the top of the charts, selling a jaw-dropping 259,000 copies in its first week.

The boys from Western Sydney have since gone on to pick up a string of accolades including New Artist Of The Year at the American Music Awards, Breakout Group at the Teen Choice Awards and Best Lyric Video at the MTV Video Music Awards.

Lots to celebrate: Bass guitarist Calum Hood celebrated his 19th birthday at a party on Saturday

Lots to celebrate: Bass guitarist Calum Hood celebrated his 19th birthday at a party on Saturday

On Saturday, 160,000 fans favourited a tweet of Calum's calling on his followers to 'have a drink' for his 19th birthday.

'Everyone currently needs to have a drink right now because its my birthday no excuses,' he said.

His band mate Michael also wished him a happy birthday on Twitter writing: 'Happy birthday to the man the myth the legend @Calum5SOS,' a message that garnered 120,000 favourites and 100,000 retweets.

Meanwhile Luke donned an oversized bow tie in honour of the occasion, and enjoyed a night on the town with Calum at a private party.

Popular star: 160,000 fans favourited his tweet calling them to have a drink in his honour

Popular star: 160,000 fans favourited his tweet calling them to have a drink in his honour

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