It's possible that a small scab in a straight line on your lip could be due to herpes, especially if you've had cold sores before. Herpes simplex virus (HSV) can sometimes cause tiny blisters or ulcers which may then scab over as they heal. However, without pain, swelling, or redness accompanying the scab, it might also be related to some other type of injury like accidentally biting your lip or minor trauma from something else. If you're concerned about it being herpes and want peace of mind, consider getting tested just to confirm whether it's HSV-related or not!