How to tell if TDE (encryption) has been enabled on a SQL server

Say you inherited a pile of SQL servers.  How do you tell if a database has ever been encrypted on any of them?

Run this query on each server.  For bonus points, use something like Idera Multi Query so it runs against all the servers at once.  Multi Query is part of Idera's SQL Admin Toolset.

select [name], is_master_key_encrypted_by_server, is_encrypted

from master.sys.databases

go

Another approach is to view the symmetric keys:

select
        [name]
      , [principal_id]
      , [algorithm_desc]
      , [create_date]
from master.sys.symmetric_keys

If a master key exists, you will find one of the [name] fields populated with "##MS_DatabaseMasterKey##"