You can look for varbinary columns. It's not a perfect indicator as other things can require varbinary (eg files), but encrypted data must go into varbinary columns.
There's no specific flags for encrypted columns (and selecting from the tables won't necessarily tell you they're encrypted), because encryption is not a table/column attribute, it's just something you do to data before inserting it.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability