Their professionals look into a business's situation and determine a bond ranking for the business. Every rating service has its own formula for determining risk and its own type of score scale. Generally, score scales are defined in letter grades, where an AAA score designates a safe, low-risk bond, and a D score designates a high-risk bond.federal government bonds, are usually low-yield bonds. You can depend upon getting a payout but that payment will be little. how is a bond represented in the yahoo finance. On the other side of the spectrum, you have what's not-so-affectionately referred to as, which are low-rated, high-risk bonds. In order to entice investors into purchasing these dangerous scrap bonds, the issuing companies assure high yields.