Graffiti in Germany is not like graffiti in the US, so please don't feel like you should be frightened to walk in areas based on the amount of graffiti that is seen. The only gangs that are here are the ones running the RLD, like the Banditos or some of the Mafia groups, and they are not wasting time writing slogans on bridges, buildings or trains.
As an older woman, I truly have no qualms about walking anywhere in Germany, down any street and at any time of the day or night, and I do NOT feel like it is less safe than 30 years ago. Remember, I live in the city that is supposed to have the highest crime rate too. Yet, I know I can walk through the RLD and no one will bother me. It is unsavory and I feel horribly sad for the people that live or work here, but they are not going to hurt me or steal from me.
If you would like to know the scariest places? Rural train stations, out in the country, late at night. With bored, drunk teens who have nothing to do but vandalize.