There’s a video of Claire Foy circulating online right now of her passing by fans who are waiting to catch a glimpse of the star, and some, who want her autograph.

In the video, the 39-year-old All of Us Strangers star is asked by one man to sign an autograph. He’s holding a blue pen, and she tells him, “I don’t do blue.” She then keeps moving and signs an autograph for another onlooker who has a black sharpie.

Commenters are now explaining why Claire Foy likely passed up the autograph request for the person holding the blue ink.

Keep reading to find out more…

“Most celebrities and athletes are taught not to do blue ink cause you can scan and forge the signature on other things and sell them,” one commenter wrote on Instagram, amassing nearly 4,000 “likes” on the comment.

Another commenter wrote, “1. Colored ink autographs get sold for far more money on eBay etc. Some celebs don’t want to support a secondary market/exploitation of their brand. 2. Sometimes legal documents require blue ink bc black is too easy to copy/reproduce so celebs are taught to only sign in black so it’s not easily transferred (same reason why many won’t sign blank white paper, to easy to transfer.)”

If you want to see the video in question, head to Instagram.

If you don’t know, while Claire happily did sign autographs in black ink…some celebs refuse to sign at all!