Why was Lawrencium's symbol changed?
Ghiorso, Sikkeland, Larsh, and Latimer of the Lawrence Berkeley Laboratory reported the discovery of element 103 in 1961. It is correct that the discoverers suggested the name lawrencium, symbol Lw, for the new element in honor of E. O. Lawrence, inventor of the cyclotron and founder of the Lawrence Berkeley Laboratory. The original proposal can be found in Ghiorso, A.; Sikkeland, T., Larsh, A. E.; Latimer, R. M. New Element, Lawrencium, Atomic Number 103. Phys. Rev. Lett. 1961, 6 (9), 473–475:


  In honor of the late Ernest O. Lawrence, we respectfully suggest that the new element be named lawrencium with the symbol Lw.


At the XXII Conference of the IUPAC in London 1963, the name was accepted but the symbol was changed to Lr. According to Comptes rendus / XXII Conference, London 5th to 9th July, 1963, the reason was simply the difficulty with the letter “w”:


  Following the observation by H. Remy that “w” is an uncommon letter in many languages and difficult to pronounce it was proposed to alter the spelling to Laurentium. The Chairman emphasized that the Commission had no right to modify the spelling of the name, but that it could be pronounced according to the custom of the language. To make the name more acceptable it was decided to recommend the chemical symbol Lr and not Lw for element 103.