A US woman was horrified to discover she'd let her young son wear a graphic sexual T-shirt to school.

Shelley McCullar, from Texas, posted a photo to Facebook of her son Anthony wearing a red shirt with a large yellow design on the front.

At first glance the image looks like the famous 'golden arches' logo of fast food chain McDonald's.

On closer inspection, however, the T-shirt is clearly designed to resemble a woman's open legs - lending quite a different meaning to the slogan 'I'm lovin' it', which is printed below.

Ms McCullar says she was extremely embarrassed when she realised the raunchy meaning behind the shirt, which Anthony had worn to his school, Travis Elementary.