In general Riga is a quiet and safe city where you are unlikely to have any trouble.
When visiting bars and restaurants make sure you know the price before you order and keep track of your spending, so no cheating is possible. Beware of scammers who strike up conversations out of the blue and invite you to visit their favorite club or bar; this is often a favorite way for the fraudsters to rob the foreigners, and the police are unlikely to help if you get scammed.
US embassy has issued travel advisory for clubs and bars in Riga which are involved in crimes against foreign clientele. For whole report please read this page (http://riga.usembassy.gov...) from US Embassy includes a list of establishments involved. See the infobox near the Drink section for a common scam run in Riga.
