Answer :
Explanation :

8 S on SS means 8 Sides on a Stop Sign. This is one type of Letter Equations which are well known phrases or facts where the key words have been replaced with the first letter of that word. These are often in the form of an equation, which contain a number, an = sign and the rest of the obscured phrase or fact.   Some more of them are :: 90 D in a RA 26 L of the A  12 S of the Z.