CHARLOTTE, N.C. – Vani Hari had a tube of lipstick, a front-row seat and a message.

Amid the sea of blue and white signs waved by thousands of delegates at the Democratic National Convention, the 33-year-old North Carolina delegate stood with her “Forward” sign held high, crowned by the words “Label GMOs!” written in lipstick red.

As a delegate from the convention’s host state, Ms. Hari has a seat near the stage each night. On Tuesday, armed only with her lipstick, a shade called True Blood, Ms. Hari said the sign alteration, intended to highlight the concerns about foods produced from genetically modified organisms, or GMOs, came as a spur-of-the-moment idea.

“I thought, whoa, here’s an opportunity to spread awareness about labeling GMOs, which street-corner protests couldn’t even compare to doing it right in front of the first lady,” she said Wednesday, as she revealed a large bag of permanent markers from her purse, planned for the night’s speeches.

“I am not afraid to tell people what’s in their food,” she said. “Every American needs to know that 90 percent of the processed foods they eat are genetically modified.”