Determining Database Role Of Querying User

I know that I can use:

IS_MEMBER('MyRoleName') = 1

to determine if a user is a member of a predetermined role, but how do I ask what the role name of the querying user is instead? Basically I want to do something like:

SELECT * FROM CityTable WHERE City IN (SELECT City FROM CitySecurity WHERE SelectGroup = ROLE_NAME)

I'm doing this because the "CitySecurity" table contains security information from another system that has been imported into SQL Server, where the 'SelectGroup', as part of process, will be named the same as the SQL Server role.

Thanks,
Kayda