What does the e3 or e4 printed on an IC mean?
It is regarding the lead content or plating finish.  Here is an excerpt from IPC/JEDEC J-STD-609:


  e0 - contains intentionally added lead (Pb)
  
  e1 - SnAgCu (shall not be included in category e2)
  
  e2 - Sn alloys with no Bi or Zn excluding SnAgCu
  
  e3 - Sn
  
  e4 - Preplated (e.g., Ag, Au, NiPd, NiPdAu)
  
  e5 - SnZn, SnZnx (no Bi)
  
  e6 - contains Bi
  
  e7 - low temperature solder (\$\le\$ 150C) containing Indium (no Bi)
  
  e8, e9 - unassigned