Glitter nail polish is literally the first item discussed in the article linked by the parent poster, with the claim notably being: "With the first two methods

Glitter nail polish is literally the first item discussed in the article linked by the parent poster, with the claim notably being: "With the first two methods [of applying glitter nail polish], it is sometimes very difficult or even impossible to detect manipulations. However, a thorough approach can increase the chances." Additionally, glitter nail polish is specifically what's written in the OP post (by the Librem team).