Yes, depending on the situation. When she does a formal signing for Star Wars Authentics, or isn't rushed, she'll use her full name. But in almost all cases where she's on the street signing for a crowd, she'll just use the first name. She also signed a lot of official Star Wars trading cards with the first name only. It's probably her most common style.
The one thing that I've noticed about Daisy's signatures is that it's usually very small on the photo. This one seems rather larger than her usual signature.