Contostavlos' arm tattoo reads 'The Female Boss'. It can usually be seen when she brings her arm up horizontally at the start of the show in what has become her signature move. But on Sunday she covered up the tattoo.
Contostavlos has had the tattoo since January. It is believed to refer to her role in the band N-Dubz, but it is also the name of the perfume she launched in October.
Last week, Ofcom announced it had launched an investigation into whether an episode of The Xtra Factor on 29 October, an episode of The X Factor Results on 6 November and an episode of The X Factor on 12 November broke its rules.
In The X Factor Results on 6 November Contostavlos' perfume was discussed and the show cut to a shot of her arm.
It is understood two people submitted complaints. One complained about The Xtra Factor episode and one complained about both The X Factor Results and The X Factor.
Ofcom will consider whether The X Factor broke either rule 9.4 (products, services and trademarks must not be promoted in programming) or rule 9.5 (no undue prominence must be given to a product service or trademark) of the Broadcasting Code.