Place potatoes in a large saucepan and cover with cold water. Bring to a gentle boil on medium-high heat. Cook for 8-10 minutes, or until fork-tender. Drain and let cool completely.
Reserve 1 tablespoon of diced red onion. In a large bowl, mix mayonnaise, mustard, vinegar and OLD BAY until well combined. Add potatoes, eggs and remaining red onion to bowl and toss to coat well.
Cover and refrigerate for at least 1 hour, or until ready to serve. Sprinkle with chives and reserved red onion before serving. If desired, sprinkle with additional OLD BAY.