The £60 design is thought to be a show of her commitment to husband Chris Martin, 31.
The actress spent an hour browsing through a catalogue of letters and Roman numerals at Zulu in Selfridges, London, before picking out the body art.
'Gwyneth came in last week,' a member of staff told the Sunday Mirror.
'But we don't comment on the work that clients have done. A lot of celebrities have visited us.'
Gwyneth, 35, and Chris have 2 children – daughter Apple, 3, and son Moses, 23 months.
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