If it looks like a small black eye winking at you, you need a new tire. The two main causes of this are impact damage form sharp corners, like potholes, driveway curbs, or steel plates over road work, and abrasion from a brake shoe mounted too high and cutting into the tire over time.

If it's not the brake shoe, you'll continue to suffer this kind of damage unless you learn to help the bike over bumps by standing with your knees bent to act like a suspension system so the bike can lift without lifting you too. Larger cross section tires will also help, but aren't a replacement for good riding habits.