Yes, it is a sign. It's the milk ducts preparing for breast feeding. It becomes a lot more prominent at about 9 weeks, 4 weeks after your missed period
Pregnancy symptoms are different for every women. The most common symptom regarding the breasts are swollen, sore or tender breasts which usually happens as early as 1-2 weeks after conception.
(Disclaimer: symptons vary. consult your doctor, local health department or planned parenthood for more information. This list is not all-inclusive. Go to webmd for more information or google...