One of the many things that HHH has been used for is, indeed, the regional airport code identifier for the airport at Hilton Head island, South Carolina.
The airport code for Evans Head Memorial Aerodrome is EVH.
The airport code for Jammu Airport is IXJ.
The airport code for Zagreb Airport is ZAG.
The airport code for Shannon Airport is SNN.
The airport code for Miyako Airport is MMY.
Honolulu, HI - Honolulu Airport (HNL).
The airport code for Gao International Airport is GAQ.
The airport code for Altay Airport is AAT.
The airport code for Munich Airport is MUC.
The airport code for Tandag Airport is TDG.
The airport code for Hokitika Airport is HKK.