Public toilets are not as widespread in St Petersburg as in many European cities. That said, you can often find a bank of portacabins outside the major metro stations, and for about RUB20 you can use these facilities. Otherwise if you're caught short, a friendly and/or apologetic smile to the staff in any coffee shop or fast food restaurant should be enough for them to point out where their toilets are located. The Russian word for toilets is ТУАЛЕТЫ (although you may often see the English letters WC used too), and the signs to indicate male and female are М(ужчины) and Ж(енщины) respectively. Many visitors also carry round some toilet paper with them, just in case, although this is less of a problem in the city center. Bear in mind that even in the nicest establishments, many toilets are unisex so be prepared to find yourself waiting in line or washing your hands with members of the opposite sex.