It's American odds. Negative means bet $100 to win that amount, positive means bet that amount to win $100. In other words:
+100: bet $100 to win $100
+5000: bet $100 to win $500
+20,000: bet $100 to win $20,000
-100: bet $100 to win $100
-1000: bet $1000 to win $100
-50,000: bet $50,000 to win $100