I'm assuming that the sticker in your rear window is your State Registration sticker. An automobile is registered for one year, and the registration has to be renewed every year. The date on the sticker is the expiration date of the Registration, and yours is about to expire in Feb. 2019. Take your Title and proof of insurance and go down and re-register your car. You will be issued a new Registration sticker.
Many states require that your car be inspected at a State-authorized Inspection Station every year. In those states, the Inspection is entirely separate from the Registration, and they may not both expire on the same date. The Inspection sticker is a different sticker than your Registration sticker. I don't know what the Inspection/Registration process entails in your state, because I don't know where you live.
I don't know if you need to go to the DMV office or if you don't, because I don't know what state you're in. In my state (Texas), registration is done at the County Tax Assessor/Collector's office (the Texas DMV doesn't register cars); or it can be done at some other authorized location (such as a local independent insurance agency). If might be done somewhat differently in your mystery state. Phone your state's DMV office, and they can probably tell you the name of an authorized location where you can re-register your car.
You should have received a renewal notice from your state's DMV a couple of months ago. I'm going to assume that you registered the car in YOUR name at the time you bought it. If you didn't, you were supposed to. If you didn't, the sticker that is now on the back window was issued to the previous owner. If you haven't ever registered the car in your name, the previous owner is still shown as the registered owner, in the DMV's data base; and renewal notices have been mailed to HIM. He's been ignoring them because he no longer owns the car.
You have, in effect, be driving around in a car with an invalid registration sticker ever since May 2018. You're going to have to personally go to the County Tax Assessor's office with your Title and proof of insurance and register the car in YOUR name, in order to get it out of HIS name.