Letter designations for aviation qualifications are as follows:

A Airplane
C Commercial Pilot
G Glider
H Helicopter
I Instrument
L Land
P Private Pilot
S Seaplane
AD Aircraft Dispatcher
IA Inspection Authorization
ME Multi-Engine
SE Single-Engine
A&P Airframe and Powerplant Maintenance Technician
AGI Advanced Ground Instructor
ATP Airline Transport Pilot
BGI Basic Ground Instructor
CFI Certified Flight Instructor
CTO Control Tower Operations
DME Designated Mechanic Examiner
DWE Designated Written Examiner
GROL General Radiotelephone Operator License
HTA Heavier Than Air
IGI Instrument Ground Instructor
LTA Lighter Than Air
SME Single- and Multi-Engine
FCC Federal Communication Commission
FE Flight Engineer