"МУ" - Murmansk province (Russia)
"МШ" - Mangyshlak province (Kazakhstan)
"НБ" - Novosibirsk province (Russia), last series after "НC"
"НИ" - Nikolaev province (Ukraine)
"НО" - Novgorod province (Russia)
"НР" - Naryn province (Kyrgyzstan)
"НС" - Novosibirsk province (Russia), first series before "НБ"
"НТ" - Krasnovodsk province (Turkmenistan)
"ОБ" - Orenburg province (Russia), first series before "ОГ"
"ОГ" - Orenburg province (Russia), last series after "ОБ"
"ОД" - Odessa province (Ukraine), first series before "ОЕ"
"ОЕ" - Odessa province (Ukraine), last series after "ОД"
"ОМ" - Omsk province (Russia)
"ООТ" - Kuibishev province (currently Samara, Russia), series for vehicles traveling outside of USSR
"ОР" - Oryol province (Russia)
"ОТР" - Belarus republic, series for vehicles traveling outside of USSR
"ОШ" - Osh province (Kyrgyzstan)
"ПА" - Pavlodar province (Kazakhstan)
"ПЕ" - Penza province (Russia)
"ПК" - Primorye territory (Russian far east), last series after "ПР"
"ПМ" - Perm province (Russia), first series before "ПТ"
"ПО" - Poltava province (Ukraine)
"ПР" - Primorye territory (Russian far east), first series before "ПК"
"ПРОБА" - special series for experimental vehicles (pronounced like "proba")
"ПС" - Pskov province (Russia)
"ПТ" - Perm province (Russia), last series after "ПМ"
"РВ" - Rovno province (Ukraine)
"РД" - Rostov province (Russia), second series after "РО" and before "РП"
"РО" - Rostov province (Russia), first series before "РД"
"РЯ" - Ryazan province (Russia)
"СА" - Saratov province (Russia), first series before "СЖ"
"СБ" - Dushanbe province (Stalinabad until 1961, Tajikistan)
СВ" - Sverdlovsk province (Russia), first series before "СФ"
"СГ" - Volgograd province (formerly Stalingrad, Russia), first series before "ВГ"
"СЕ" - North-Ossetia autonomous republic (Russia)
"СЖ" - Saratov province (Russia), second series after "СА"
"СИ" - Syrdarya province (Uzbekistan)
"СК" - North-Kazakhstan province (Kazakhstan)
"СЛ" - Stalino province (from 1961 - Donetsk province, Ukraine)
"СМ" - Smolensk province (Russia)
"СН" - Samarkand province (Uzbekistan)
"СО" - Sochi and suburbs (Russia)
"СП" - Semipalatinsk province (Kazakhstan)
"СС" - Stavropol territory (Russia), second series after "СТ"
"СТ" - Stavropol territory (Russia), first series before "СС"
"СУ" - Sumy province (Ukraine)
"СФ" - Sverdlovsk province (Russia), second series after "СВ"
"СХ" - Sakhalin province (Russia)
"СЯ" - Ivano-Frankovsk province (Stanislav until 1961, Ukraine), first series before "ИФ"
"ТА" - Tambov province (Russia)
"ТБ" - Tatar autonomous republic (Russia), second series after "ТТ"
"ТЕ" - Ternopol province (Ukraine)
"ТК" - Taldy-Kurgan province (Kazakhstan)
"ТЛ" - Tula province (Russia), last series after "ТУ"
"ТМ" - Tyumen province (Russia), last series after "ТЮ"
"ТН" - Tashkent city (Uzbekistan)
"ТО" - Tomsk province (Russia)
"ТР" - Turkmenia republic (before it was divided to provinces in early 70-s)
"ТСК"- Tula province, series for vehicles traveling outside of USSR
"ТСН"- Tyumen province, series for vehicles traveling outside of USSR
"ТСТ" - Tatar autonomous republic (Russia), series for vehicles traveling outside of USSR
"ТТ" - Tatar autonomous republic (Russia), first series before "ТБ"
"ТУ" - Tula province (Russia), first series before "ТЛ"
"ТЮ" - Tyumen province (Russia), first series before "ТМ"
"ТЯ"- Tyan-Shan province (after mid-60's Frunze province, Kyrgyzstan)
"УД" - Udmurtia autonomous republic (Russia)
"УК" - Kuibishev province (currently Samara, Russia), second series after "КШ"
"УЛ" - Ulyanovsk province (Russia)
"ФИ" - Frunze province (currently Bishkek, Kyrgyzstan)
"ХА" - Kharkov province (Ukraine), first series before "ХК"
"ХБ" - Khabarovsk territory (Russia)
"ХЗ" - Khoresm province (Uzbekistan)
"ХК" - Kharkov province (Ukraine), last series after "ХА"
"ХМ" - Khmelnitsky province (Ukraine)
"ХО" - Kherson province (Ukraine)
"ХТ" - Kiev city (Ukraine), last series after "КИ"
"ЦВ" - Krasnodar territory (Russia), last series after "ЦП"
"ЦП" - Krasnodar territory (Russia), second series after "КК" before "ЦВ"
"ЦС" - Crimea province (Ukraine), second series after "КР"
"ЧБ" - Cheliabinsk province (Russia), second series after "ЧЕ"
"ЧВ" - Chernovtsy province (Ukraine)
"ЧЕ" - Cheliabinsk province (Russia), first series before "ЧБ"
"ЧИ" - Chechen-Ingush autonomous republic (Russia)
"ЧК" - Cherkasy province (Ukraine)
"ЧН"- Chernigov province (Ukraine)
"ЧТ" - Chita province (Russia)
"ЧУ" - Chuvashia autonomous republic (Russia)
"ЭС" - Estonia, first series before "ЕА"
"ЮА" - Moscow province (without Moscow city)
"ЮБ" - Moscow province (without Moscow city)
"ЮВ" - Moscow province (without Moscow city)
"ЮГ" - Moscow province (without Moscow city)
"ЮК" - South-Kazakhstan province (Kazakhstan)
"ЮМЭ" - Moscow province (without Moscow city). Was issued instead of "ЮАЭ" series.
"ЯК" - Yakutia autonomous republic (currently Sakha, Russia)
"ЯР" - Yaroslavl province (Russia)