From the Dictionary Of Jewish Surnames From The Russian Empire. The name Ramm was common in Shavli, Riga, Polotsk. The name Ram was common in Vilna and Poolotski ( Ramm, Ram, Rom, Romm, Room, Rum, Romov )
The name Ramm is an acronym : Rauveyn Manshes, ( Hebrew) Reuben Manshes or Rabij Mnaheym Man (Hebrew) Rabbi Menahem Man (Rabiovich)
To explain that the name 'Ramm' when written out in Hebrew is an abbreviation for several other names:
In each case the first letter begins with the letter Resh (letter R) and the second letter begins with the letter Mem (letter M). So for example, the name Reuben Manshes would be abbreviated as R"M in Hebrew (which is pronounced Ramm).