This is your best choice. Add this extension to the file area and you can customize the icons as you like. Just call self.tabBarController!.setBadges([1,0,2])in any of your root controllers.

, , .

, addBadge

extension UITabBarController {
    func setBadges(badgeValues:[Int]){

        var labelExistsForIndex = [Bool]()

        for value in badgeValues {
            labelExistsForIndex.append(false)
        }

        for view in self.tabBar.subviews {
            if view.isKindOfClass(PGTabBadge) {
                let badgeView = view as! PGTabBadge
                let index = badgeView.tag

                if badgeValues[index]==0 {
                    badgeView.removeFromSuperview()
                }

                labelExistsForIndex[index]=true
                badgeView.text = String(badgeValues[index])

            }
        }

        for var i=0;i<labelExistsForIndex.count;i++ {
            if labelExistsForIndex[i] == false {
                if badgeValues[i] > 0 {
                    addBadge(i, value: badgeValues[i], color:UIColor(red: 4/255, green: 110/255, blue: 188/255, alpha: 1), font: UIFont(name: "Helvetica-Light", size: 11)!)
                }
            }
        }


    }

    func addBadge(index:Int,value:Int, color:UIColor, font:UIFont){

        let itemPosition = CGFloat(index+1)
        let itemWidth:CGFloat = tabBar.frame.width / CGFloat(tabBar.items!.count)

        let bgColor = color

        let xOffset:CGFloat = 12
        let yOffset:CGFloat = -9

        var badgeView = PGTabBadge()
        badgeView.frame.size=CGSizeMake(17, 17)
        badgeView.center=CGPointMake((itemWidth * itemPosition)-(itemWidth/2)+xOffset, 20+yOffset)
        badgeView.layer.cornerRadius=badgeView.bounds.width/2
        badgeView.clipsToBounds=true
        badgeView.textColor=UIColor.whiteColor()
        badgeView.textAlignment = .Center
        badgeView.font = font
        badgeView.text = String(value)
        badgeView.backgroundColor = bgColor
        badgeView.tag=index
        tabBar.addSubview(badgeView)

    }
}

class PGTabBadge: UILabel {

}

Here is another solution based on TimWhiting's answer :

extension UITabBar {
        func setBadge(value: String?, at index: Int, withConfiguration configuration: TabBarBadgeConfiguration = TabBarBadgeConfiguration()) {
            let existingBadge = subviews.first { ($0 as? TabBarBadge)?.hasIdentifier(for: index) == true }
            existingBadge?.removeFromSuperview()

            guard let tabBarItems = items,
                let value = value else { return }

            let itemPosition = CGFloat(index + 1)
            let itemWidth = frame.width / CGFloat(tabBarItems.count)
            let itemHeight = frame.height

            let badge = TabBarBadge(for: index)
            badge.frame.size = configuration.size
            badge.center = CGPoint(x: (itemWidth * itemPosition) - (0.5 * itemWidth) + configuration.centerOffset.x,
                                   y: (0.5 * itemHeight) + configuration.centerOffset.y)
            badge.layer.cornerRadius = 0.5 * configuration.size.height
            badge.clipsToBounds = true
            badge.textAlignment = .center
            badge.backgroundColor = configuration.backgroundColor
            badge.font = configuration.font
            badge.textColor = configuration.textColor
            badge.text = value

            addSubview(badge)
        }
    }

    class TabBarBadge: UILabel {
        var identifier: String = String(describing: TabBarBadge.self)

        private func identifier(for index: Int) -> String {
            return "\(String(describing: TabBarBadge.self))-\(index)"
        }

        convenience init(for index: Int) {
            self.init()
            identifier = identifier(for: index)
        }

        func hasIdentifier(for index: Int) -> Bool {
            let has = identifier == identifier(for: index)
            return has
        }
    }

    class TabBarBadgeConfiguration {
        var backgroundColor: UIColor = .red
        var centerOffset: CGPoint = .init(x: 12, y: -9)
        var size: CGSize = .init(width: 17, height: 17)
        var textColor: UIColor = .white
        var font: UIFont! = .systemFont(ofSize: 11) {
            didSet { font = font ?? .systemFont(ofSize: 11) }
        }

        static func construct(_ block: (TabBarBadgeConfiguration) -> Void) -> TabBarBadgeConfiguration {
            let new = TabBarBadgeConfiguration()
            block(new)
            return new
        }
    }