Polyhedral symbol (sometimes used in coordination chemistry) has 25 symbols one of which is Trigonal Planar.
L-2 A-2 TP-3 TPY-3 TS-3 T-4 SP-4 SPY-4 SS-4 TBPY-5 SPY-5 OC-6 TPR-6 PBPY-7 OCF-7 TPRS-7 CU-8 SAPR-8 DD-8 HBPY-8 OCT-8 TPRT-8 TPRS-8 TPRS-9 HBPY-9 
