O que é Rj:
Sigla de RIO DE JANEIRO (ESTADO): O plural de RJ é RJs.

Cá está uma lista de siglas de placas de carros do Estado do RJ (do KMA-0000 ao LUZ-9999):

KMA, KMB, KMC, KMD, KME, KMF, KMG, KMH, KMI, KMJ, KMK, KML, KMM, KMN, KMO, KMP, KMQ, KMR, KMS, KMT, KMU, KMV, KMW, KMX, KMY, KMZ, KNA, KNB, KNC, KND, KNE, KNF, KNG, KNH, KNI, KNJ, KNK, KNL, KNM, KNN, KNO, KNP, KNQ, KNR, KNS, KNT, KNU, KNV, KNW, KNX, KNY, KNZ, KOA, KOB, KOC, KOD, KOE, KOF, KOG, KOH, KOI, KOJ, KOK, KOL, KOM, KON, KOO, KOP, KOQ, KOR, KOS, KOT, KOU, KOV, KOW, KOX, KOY, KOZ, KPA, KPB, KPC, KPD, KPE, KPF, KPG, KPH, KPI, KPJ, KPK, KPL, KPM, KPN, KPO, KPP, KPQ, KPR, KPS, KPT, KPU, KPV, KPW, KPX, KPY, KPZ, KQA, KQB, KQC, KQD, KQE, KQF, KQG, KQH, KQI, KQJ, KQK, KQL, KQM, KQN, KQO, KQP, KQQ, KQR, KQS, KQT, KQU, KQV, KQW, KQX, KQY, KQZ, KRA, KRB, KRC, KRD, KRE, KRF, KRG, KRH, KRI, KRJ, KRK, KRL, KRM, KRN, KRO, KRP, KRQ, KRR, KRS, KRT, KRU, KRV, KRW, KRX, KRY, KRZ, KSA, KSB, KSC, KSD, KSE, KSF, KSG, KSH, KSI, KSJ, KSK, KSL, KSM, KSN, KSO, KSP, KSQ, KSR, KSS, KST, KSU, KSV, KSW, KSX, KSY, KSZ, KTA, KTB, KTC, KTD, KTE, KTF, KTG, KTH, KTI, KTJ, KTK, KTL, KTM, KTN, KTO, KTP, KTQ, KTR, KTS, KTT, KTU, KTV, KTW, KTX, KTY, KTZ, KUA, KUB, KUC, KUD, KUE, KUF, KUG, KUH, KUI, KUJ, KUK, KUL, KUM, KUN, KUO, KUP, KUQ, KUR, KUS, KUT, KUU, KUV, KUW, KUX, KUY, KUZ, KVA, KVB, KVC, KVD, KVE, KVF, KVG, KVH, KVI, KVJ, KVK, KVL, KVM, KVN, KVO, KVP, KVQ, KVR, KVS, KVT, KVU, KVV, KVW, KVX, KVY, KVZ, KWA, KWB, KWC, KWD, KWE, KWF, KWG, KWH, KWI, KWJ, KWK, KWL, KWM, KWN, KWO, KWP, KWQ, KWR, KWS, KWT, KWU, KWV, KWW, KWX, KWY, KWZ, KXA, KXB, KXC, KXD, KXE, KXF, KXG, KXH, KXI, KXJ, KXK, KXL, KXM, KXN, KXO, KXP, KXQ, KXR, KXS, KXT, KXU, KXV, KXW, KXX, KXY, KXZ, KYA, KYB, KYC, KYD, KYE, KYF, KYG, KYH, KYI, KYJ, KYK, KYL, KYM, KYN, KYO, KYP, KYQ, KYR, KYS, KYT, KYU, KYV, KYW, KYX, KYY, KYZ, KZA, KZB, KZC, KZD, KZE, KZF, KZG, KZH, KZI, KZJ, KZK, KZL, KZM, KZN, KZO, KZP, KZQ, KZR, KZS, KZT, KZU, KZV, KZW, KZX, KZY, KZZ, LAA, LAB, LAC, LAD, LAE, LAF, LAG, LAH, LAI, LAJ, LAK, LAL, LAM, LAN, LAO, LAP, LAQ, LAR, LAS, LAT, LAU, LAV, LAW, LAX, LAY, LAZ, LBA, LBB, LBC, LBD, LBE, LBF, LBG, LBH, LBI, LBJ, LBK, LBL, LBM, LBN, LBO, LBP, LBQ, LBR, LBS, LBT, LBU, LBV, LBW, LBX, LBY, LBZ, LCA, LCB, LCC, LCD, LCE, LCF, LCG, LCH, LCI, LCJ, LCK, LCL, LCM, LCN, LCO, LCP, LCQ, LCR, LCS, LCT, LCU, LCV, LCW, LCX, LCY, LCZ, LDA, LDB, LDC, LDD, LDE, LDF, LDG, LDH, LDI, LDJ, LDK, LDL, LDM, LDN, LDO, LDP, LDQ, LDR, LDS, LDT, LDU, LDV, LDW, LDX, LDY, LDZ, LEA, LEB, LEC, LED, LEE, LEF, LEG, LEH, LEI, LEJ, LEK, LEL, LEM, LEN, LEO, LEP, LEQ, LER, LES, LET, LEU, LEV, LEW, LEX, LEY, LEZ, LFA, LFB, LFC, LFD, LFE, LFF, LFG, LFH, LFI, LFJ, LFK, LFL, LFM, LFN, LFO, LFP, LFQ, LFR, LFS, LFT, LFU, LFV, LFW, LFX, LFY, LFZ, LGA, LGB, LGC, LGD, LGE, LGF, LGG, LGH, LGI, LGJ, LGK, LGL, LGM, LGN, LGO, LGP, LGQ, LGR, LGS, LGT, LGU, LGV, LGW, LGX, LGY, LGZ, LHA, LHB, LHC, LHD, LHE, LHF, LHG, LHH, LHI, LHJ, LHK, LHL, LHM, LHN, LHO, LHP, LHQ, LHR, LHS, LHT, LHU, LHV, LHW, LHX, LHY, LHZ, LIA, LIB, LIC, LID, LIE, LIF, LIG, LIH, LII, LIJ, LIK, LIL, LIM, LIN, LIO, LIP, LIQ, LIR, LIS, LIT, LIU, LIV, LIW, LIX, LIY, LIZ, LJA, LJB, LJC, LJD, LJE, LJF, LJG, LJH, LJI, LJJ, LJK, LJL, LJM, LJN, LJO, LJP, LJQ, LJR, LJS, LJT, LJU, LJV, LJW, LJX, LJY, LJZ, LKA, LKB, LKC, LKD, LKE, LKF, LKG, LKH, LKI, LKJ, LKK, LKL, LKM, LKN, LKO, LKP, LKQ, LKR, LKS, LKT, LKU, LKV, LKW, LKX, LKY, LKZ, LLA, LLB, LLC, LLD, LLE, LLF, LLG, LLH, LLI, LLJ, LLK, LLL, LLM, LLN, LLO, LLP, LLQ, LLR, LLS, LLT, LLU, LLV, LLW, LLX, LLY, LLZ, LMA, LMB, LMC, LMD, LME, LMF, LMG, LMH, LMI, LMJ, LMK, LML, LMM, LMN, LMO, LMP, LMQ, LMR, LMS, LMT, LMU, LMV, LMW, LMX, LMY, LMZ, LNA, LNB, LNC, LND, LNE, LNF, LNG, LNH, LNI, LNJ, LNK, LNL, LNM, LNN, LNO, LNP, LNQ, LNR, LNS, LNT, LNU, LNV, LNW, LNX, LNY, LNZ, LOA, LOB, LOC, LOD, LOE, LOF, LOG, LOH, LOI, LOJ, LOK, LOL, LOM, LON, LOO, LOP, LOQ, LOR, LOS, LOT, LOU, LOV, LOW, LOX, LOY, LOZ, LPA, LPB, LPC, LPD, LPE, LPF, LPG, LPH, LPI, LPJ, LPK, LPL, LPM, LPN, LPO, LPP, LPQ, LPR, LPS, LPT, LPU, LPV, LPW, LPX, LPY, LPZ, LQA, LQB, LQC, LQD, LQE, LQF, LQG, LQH, LQI, LQJ, LQK, LQL, LQM, LQN, LQO, LQP, LQQ, LQR, LQS, LQT, LQU, LQV, LQW, LQX, LQY, LQZ, LRA, LRB, LRC, LRD, LRE, LRF, LRG, LRH, LRI, LRJ, LRK, LRL, LRM, LRN, LRO, LRP, LRQ, LRR, LRS, LRT, LRU, LRV, LRW, LRX, LRY, LRZ, LSA, LSB, LSC, LSD, LSE, LSF, LSG, LSH, LSI, LSJ, LSK, LSL, LSM, LSN, LSO, LSP, LSQ, LSR, LSS, LST, LSU, LSV, LSW, LSX, LSY, LSZ, LTA, LTB, LTC, LTD, LTE, LTF, LTG, LTH, LTI, LTJ, LTK, LTL, LTM, LTN, LTO, LTP, LTQ, LTR, LTS, LTT, LTU, LTV, LTW, LTX, LTY, LTZ, LUA, LUB, LUC, LUD, LUE, LUF, LUG, LUH, LUI, LUJ, LUK, LUL, LUM, LUN, LUO, LUP, LUQ, LUR, LUS, LUT, LUU, LUV, LUW, LUX, LUY, LUZ.

Clique aqui para mais definições de Rj

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