Southern Oscillation Index 
Space Object Identification 
Solar Oscillations Investigation 
signal operation instructions 
Saturn Orbit Insertion 
second order intercept 
signal of interest 
Signal Operating Instructions 
Silicon on Insulator 
Start of Image 
Statement Of Intent 
Self Owning Idiot 
Signal Operating Instruction 
silicon-on-insulator 
solar oscillations imager 
Solar Oscillations Imagery 
Spinscan Ozone Imager 
Standard Operator Interface 
State Of Insanity 
Supervisory Operations Inspector 
Survey of India 
School of Infantry 
School of Informatics 
School of Instruction 
School Of Internet 
Security Operational Inspection 
Semiconductor-on-Insulator 
Show of Interest 
Signal Operation Instruction 
Signal Operations Instructions