It just relates to the length of the facing curve. Bergs can be either M(medium) or SMS(Medium Short)
The other markings on bergs are for the chamber size(represented by the numbers 0 - 3) and the tip size in hundredths of an inch
the 0, 1, 2, or 3 on the Berg more accurately reflects the baffle height.
0 is the highest (and brightest/edgiest) and three the lowest (most nonexistant)