Find signed procedures, functions, triggers, assemblies and by which certificates / asymmetric keys
The easiest way seems to be using the sys.crypt_properties Catalog View which holds the relationship between Certificates / Asymmetric Keys and signed modules, as well as the usage (i.e. Signature or Counter-Signature). There are a few other means of finding which modules are signed, but none seem to indicate Signature vs Counter-Signature.

SELECT SCHEMA_NAME(so.[schema_id]) AS [SchemaName],
       so.[name] AS [ObjectName],
       so.[type_desc] AS [ObjectType],
       ---
       scp.crypt_type_desc AS [SignatureType],
       ISNULL(sc.[name], sak.[name]) AS [CertOrAsymKeyName],
       ---
       scp.thumbprint
FROM sys.crypt_properties scp
INNER JOIN sys.objects so
        ON so.[object_id] = scp.[major_id]
LEFT JOIN sys.certificates sc
        ON sc.thumbprint = scp.thumbprint
LEFT JOIN sys.asymmetric_keys sak
        ON sak.thumbprint = scp.thumbprint
WHERE   so.[type] &lt;&gt; 'U'
ORDER BY [SchemaName], [ObjectType], [ObjectName], [CertOrAsymKeyName];


In my test DB, this query returns the following:

Schema  ObjectName     ObjectType            SignatureType                        CertOrAsymKeyName  thumbprint
------  ----------     ----------            -------------                        -----------------  ----------
dbo     fnPaymentCalc  SQL_SCALAR_FUNCTION   COUNTER SIGNATURE BY ASYMMETRIC KEY  KeyTest1           0x2333B2FA6AA8004E
dbo     ModuleTest2    SQL_STORED_PROCEDURE  SIGNATURE BY CERTIFICATE             CrossDatabaseCert  0x49BA174584C78C878D923690C15898A809CBACDF
dbo     TestSig        SQL_STORED_PROCEDURE  SIGNATURE BY CERTIFICATE             bob                0x778B3DB4ED981FC27AB301ACE7A1AB8424F64792
dbo     TestSig        SQL_STORED_PROCEDURE  SIGNATURE BY ASYMMETRIC KEY          KeyTest1           0x2333B2FA6AA8004E