The + refers to the underdog, while the - tells you who is the favorite.
When a team is favored to win, they will receive a negative number next to their team name. For example, in Super Bowl 55, the Kansas City Chiefs were favored by 3 points over the Tampa Bay Buccaneers.
This means that oddsmakers believed the Chiefs were 3 points “superior” to the Buccaneers and therefore if you wagered on the Chiefs to win, they also had to win by 3 or more points.
The Buccaneers were a 3 point underdog so they would be referred to as +3. The Buccaneers won the game by a huge margin of 22 points, shocking many across the world as the spread was not close to accurate when compared to the results of the game. The winning bet is referred to as “Buccaneers +3” and the losing bet would be “Chiefs -3”.